


Monograph 










) 


DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, Director 


Bulletin 581—D 


GEOLOGY AND OIL PROSPECTS 

IN 

WALTHAM, PRIEST, BITTERWATER, AND 
PEACHTREE VALLEYS, CALIFORNIA 

WITH NOTES ON COAL 


BY 

ROBERT W. PACK AND WALTER A. ENGLISH 


CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II—D 



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WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1914 






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0. OF 0, 

MAY 20 j915 


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CONTENTS. 



Page. 

Introduction. 119 

Acknowledgments. 121 

Geography. 121 

Geology.' 123 

Distribution and general relations of the rocks. 123 

Granitic rocks. 126 

Jurassic (?) system. 126 

Franciscan formation. 126 

Cretaceous system. 127 

Tertiary system. 129 

Eocene and Oligocene (?) series. 129 

Miocene series. 130 

Yaqueros formation (lower Miocene). 130 

Santa Margarita (?) formation (middle Miocene). 131 

Upper Miocene formations. 132 

Distribution and character. 132 

Area southwest of the San Andreas fault. 133 

Area northeast of the San Andreas fault. 133 

Tulare formation (Pliocene).:. 134 

Quaternary system. 135 

Structure. 135 

Petroleum. 137 

Conditions in the Coalinga district. 137 

Conditions in Waltham, Priest, Bitterwater, and Peachtree valleys. 138 

Local areas. 139 

Area south of Curry Mountain. 139 

Geology and economic possibilities. 139 

Wells drilled for oil. 143 

Waltham and Priest valleys. 143 

Bitterwater and Peachtree valleys and the foothills to the west. 144 

Geology. 144 

Surface indications of petroleum. 146 

Wells drilled for oil. 147 

Economic possibilities. 149 

Outlying districts.-. 153 

Topo ranch. 153 

San Benito River valley. 154 

Coal. 455 

Occurrence and age. 155 

Eocene coal. 155 

Lower Miocene coal. 156 

Upper Miocene coal. 158 


in 













































ILLUSTRATIONS. 


Page. 

Plate V. Geologic map of the Waltham, Priest, Bitterwater, and Peachtree 

valleys, central California. 160 

Figure 3. Columnar section of rocks northeast of the San Andreas fault, cen¬ 
tral California. 124 

4. Columnar section of rocks southwest of the San Andreas fault, cen¬ 

tral California. 125 

5. Hypothetical cross section in the Jacalitos Hills, Cal., from a point 

near the south end of Curry Mountain to the Jacalitos anticline.... 141 

6. Hypothetical cross section in the western part of the Coalinga oil 

field, Cal. 142 


IV 







GEOLOGY AND OIL PROSPECTS IN WALTHAM, PRIEST, 
BITTERWATER, AND PEACHTREE VALLEYS, CALI¬ 
FORNIA. 


By Robert W. Pack and Walter A. English. 


INTRODUCTION. 

In the investigation of the California oil fields made by the 
United States Geological Survey during the last 14 years the areas 
outside of the productive fields have received special attention, with 
the view to aiding the prospector by determining, so far as may be 
possible from a study of the surface alone, the areas in which oil 
would be most likely to occur. One of the regions in which it 
seemed that such investigation would be best repaid is the foothill 
belt on the west side of San Joaquin Valley near the Coalinga oil 
field. The Coalinga field, although one of the most productive in 
California, occupies a relatively small part of this foothill belt, and 
to casual observers there seems to be no good reason why oil should 
not be found in other parts of the foothill region and even in the 
mountainous region farther w T est, which is underlain in part by many 
of the formations that underlie the productive Coalinga field. In 
order to estimate the probable value of the foothills as oil-producing 
territory, the areas both north 1 and south 2 of Coalinga along the 
border of the valley were examined, and the conclusions reached 
are given in reports alread}^ published. The mountainous region 
farther west, which seemed less promising, has until recently re¬ 
ceived scant attention, but during part of the summer and fall of 
1913 an area extending from the western border of the Coalinga 
field across the Diablo Range to the low foothills on the east side 
of Salinas Valley was examined. The present report gives the 
results obtained in this examination. The immediate reason for 
the investigation was the need of geologic data for the classification 

1 Anderson, Robert, Preliminary report on the geology and oil prospects of the Cantua- 
Panoche region, California: U. S. Geol. Survey Bull. 431, pp. 58-87, 1911. Anderson, 
Robert, and Pack, R. W., Geology and oil resources of the western border of the San 
Joaquin Valley, Cal. : U. S. Geol. Survey Bull. 603 (in preparation). 

a Arnold, Ralph, and Anderson, Robert, Geology and oil resources of the Coalinga dis¬ 
trict, California : U. S. Geol. Survey Bull. 398, 1910. 


119 






120 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

of the public land in the area that had been withdrawn from all 
forms of entry because of its possible value as oil land. As a result 
of the examination large areas of unappropriated public land have 
been restored to entry. 

The chief conclusion reached regarding the occurrence of oil is 
that most of the region shown on the map does not offer reasonable 
promise of yielding petroleum and that much of it is certainly bar¬ 
ren of oil. In general, the conditions that make it impossible to 
consider a large part of the region a prospective oil field are the 
lack of a sufficient amount of material that might reasonably be 
considered an original source of petroleum and the absence of a 
structure which would aid in the concentration of such petroleum as 
may occur in minute quantities throughout the rocks. In much of 
the region the Franciscan formation, of probable Jurassic age, 
which lies stratigraphically below any known oil-bearing beds in 
the Coast Ranges, either appears at the surface or is overlain by only 
a thin veneer of Tertiary rocks. Moreover, where Tertiary rocks 
occur they are usually closely folded and faulted and do not offer the 
same opportunity for the accumulation of oil as the broadly folded 
strata along the foothills. In parts of the region oil sands evidently 
occur beneath the surface, but in no part does it seem probable that 
any very extensive oil field awaits development. The most promis¬ 
ing areas, which lie mainly along the western boundary of the 
region shown on the map, and also other areas in which the pos¬ 
sibility that oil occurs is more slight are discussed under the heading 
“Local areas” (pp. 139-152). 

The geology of the region is described briefly, stress being laid 
chiefly upon features that are believed to have some bearing on the 
occurrence of petroleum. Of necessity, therefore, it is impossible 
to discuss here many interesting geologic features that were brought 
out in the course of the work, such as the accurate correlation of 
the various formations with those of other regions and the intricate 
structure along the San Andreas fault. Moreover, in parts of the 
region, especially in the vicinity of the San Andreas fault, the 
structure is so complex and the distribution of the formations is 
so irregular that much of the detail brought out in the field work 
can not be shown, so that many generalizations have been made 
in depicting the areal geology on a black and white map of the scale 
of that accompanying this report. In order to show more clearly 
the relation between the geology in parts of this region and that 
about Coalinga, the areal geology of a small portion of the district 
described in the Coalinga report 1 is reproduced on the map (PI. V). 

1 Arnold, Ralph, and Anderson, Robert, Geology and oil resources of the Coalinga dis¬ 
trict, California : U. S. Geol. Survey Bull. 398, 1910. 



OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 121 

ACKNOWLEDGMENTS. 

J. D. Northrop was a member of the field party during the later 
Part of the season, and many of the facts here recorded are taken 
from his notes. 

The writers take pleasure in acknowledging their grateful ap¬ 
preciation of the courtesies extended to them by the officers of the 
oil companies in furnishing data regarding the wells and by the 
inhabitants of the region on whose hospitality they had largely to 
depend in the study of a region so sparsely settled. Special acknowl¬ 
edgment is due to E. A. Starke, of the Standard Oil Co., and to 
G. C. Gester, geologist for the Kern Trading & Oil Co. 

Before this investigation was undertaken very little work had been 
done on the geology of the area, almost the only published accounts 
dealing with it being the brief note by Eldridge on the asphalt 
deposit near Lonoak 1 and incidental mention of various general 
features in a paper by Homer Hamlin on the water resources of 
Salinas Valley. 2 Besides these accounts a few unpublished notes by 
Eldridge and Hamlin have been available. 

GEOGRAPHY. 

The area studied in detail and shown on the map lies about 140 
miles southeast of San Francisco and forms a strip 40 miles long and 
11 to 14 miles wide, extending northwest and southeast diagonally 
across the Diablo Range. It includes about 500 square miles in the 
southern parts of Fresno and San Benito counties and in the eastern 
part of Monterey County. Coalinga, at the eastern end of the area, 
is the terminus of a branch of the valley line of the Southern Pacific 
Co. From Coalinga one of the main wagon roads through the 
Diablo Range leads up Waltham Valley to Priest Valley and thence 
down the valleys of Lewis and San Lorenzo creeks to King City, in 
Salinas Valley. A branch road leaving the main road above Alcalde 
Canyon leads south across Jacalitos Creek to Parkfield, and other 
branch roads pass through Peachtree Valley to the Stone Canyon coal 
mine and up Bitterwater Valley to the valley of San Benito River. 
A 6-inch pipe line, owned by the Associated Oil & Transportation 
Co., passes through Waltham, Priest, Lewis Creek, and Bitterwater 
valleys, and through it oil is pumped from Coalinga to Monterey. 

The eastern edge of this belt includes Pleasant Valley, which lies 
in the foothills that border San Joaquin Valley, at an elevation of 
about 650 feet above the sea. The southwestern part of the area 
mapped includes the low hills that border Salinas Valley, which has 

1 Eldridge, G. H., The asphalt and bituminous rock deposits of the United States: IT. S. 
Geol. Survey Twenty-second Ann. Kept., pt. 1, pp. 407-410, 1901. 

2 Hamlin, Homer, Water resources of Salinas Valley, Cal.: U. S. Geol. Survey Water- 
Supply Paper 89, 91 pp., 12 pis., 1904. 



122 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

an elevation of about 400 feet and lies 6 to 10 miles to the southwest. 
Between these two foothill belts the mountainous part of the Diablo 
Range rises gradually to altitudes of over 4,000 feet. The culminat¬ 
ing points in this part of the range are Hepsedam, which stands 4,496 
feet above the sea; Center Peak, 4,539 feet; and Smith Mountain, 
3,967 feet. 

Here as elsewhere the range is an almost perfect reflection of the 
structure. It is not composed of a single ridge but of a number of 
somewhat broken parallel ridges that separate relatively narrow 
valleys. These ridges trend obliquely to the course of the main range 
and are determined by pronounced folds or faults. Parts of tw T o such 
ridges lie in the area shown on the map. One extends from Smith 
Mountain northwestward to and beyond Charley Mountain and sepa¬ 
rates Waltham and Priest valleys from Peachtree Valley and Slack 
Canyon. The other extends from Sherman Peak through Center Peak 
to a point north of Hepsedam and separates Bitterwater, Priest, and 
Waltham valleys from the drainage basins of Los Gatos Creek and 
San Benito River. The divide which separates the waters that drain 
into Salinas Valley from those that empty into San Joaquin Valley 
and which may therefore be considered the crest of the Diablo Range 
cuts directly across these ridges. Priest and Charley valleys are two 
small faulted synclinal valleys that lie practically at the crest of the 
range. Both lie in the Salinas drainage basin, but both are being 
rapidly cut away by streams of high gradient that drain eastward 
into San Joaquin Valley. 

The climate is dry and hot in summer, particularly on the eastern 
slope of the range. A few of the larger streams carry water through¬ 
out the year, but most of them are intermittent, and nearly all the 
water contains sufficient salts to make it unpalatable. A few of the 
springs, however, particularly those in the Franciscan formation 
and in the coarse conglomerate of the Cretaceous, furnish excellent 
water. In order to obtain boiler water for the pumping stations 
along the pipe line of the Associated Oil & Transportation Co., 
several of the better springs have been developed and the water 
piped for many miles. The main supply comes from a number of 
springs near Hepsedam which furnish the water for two stations on 
Lewis Creek and one at the head of Bitterwater Valley. 

The plains and lower hills are bare except for a sparse growth of 
sagebrush and short grass. The mountainous part is more or less 
covered by chaparral, but the growth is rarely thick enough to be 
impassable. A light growth of small pine and manzanita is common 
on the outcrops of diatomaceous shale, and oaks are scattered 
throughout the region. 

The amount of level ground suitable for agriculture is small, and 
the country is used generally as a cattle range, for despite the dry 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 123 

climate there is a good growth of grass in wet seasons. In Bitter- 
water, Priest, and Peachtree valleys and in some of the small valleys 
tributary to Salinas Valley several thousand acres are dry farmed; 
and on San Lorenzo Creek, both near Lonoak and just west of the 
area shown on the map, small areas of alfalfa are under irrigation. 

GEOLOGY. 

DISTRIBUTION AND GENERAL RELATIONS OF THE ROCKS. 

The area shown on the map (PI. V), forming a narrow belt that 
extends across the Diablo Range, does not present a single type of 
structure but is divided by the San Andreas fault into two parts, 
which are so distinct, both structurally and stratigraphically, that 
they may almost be regarded as distinct geologic provinces. The 
difference in the stratigraphic section exposed in the two parts of the 
region may be seen by comparing the two columnar sections (figs. 3 
and 4). Southwest of the fault are the foothills that border Salinas 
Valley, and northeast of it is the main Diablo Range. This range 
may also be considered as composed of two parts—the central 
mountain mass, an area of many short irregular folds and faults, 
and the eastern foothills, an area in which the rocks are flexed into 
a few broad folds. This separation is indefinite, however, as the 
structure becomes gradually more complex westward from the edge 
of San Joaquin Valley toward the mountains, and a sharp line of 
division, such as that of the San Andreas fault, is nowhere apparent. 

On the southwest side of this fault much or probably all of the 
region is underlain at no great depth by granitic rocks. These 
rocks are exposed only in small areas in the northwest corner of the 
region mapped, but farther north they appear at the surface for 
about 40 miles and form the Gabilan Range. Resting upon the 
eroded surface of this granitic mass are late Tertiary sand, clay, and 
diatomaceous shale. These beds, although tilted to low angles whose 
direction of dip is somewhat irregular, disclose few well-marked 
folds. The lower part of these late Tertiary beds is believed to be 
the equivalent of the Santa Margarita formation (middle Miocene), 
which is typically developed in the upper end of Salinas Valley, 
some 40 miles to the south. Their upper part, represented mainly 
by relatively thin deposits of gravel and clay on the flat-topped 
ridges, is correlated with the Tulare formation (Pliocene). 

Northeast of the San Andreas fault granite does not appear, and 
the oldest rocks are those of the Franciscan formation (Jurassic?). 
As mapped, this formation comprises a rather heterogeneous mass of 
more or less altered sedimentary rocks and various igneous rocks that 
are intruded into them. Strictly speaking the igneous rocks are not 
a part of the Franciscan, but for convenience in the present discussion 


124 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II 


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(Pliocene) 600 feet 


Upper Miocene 
formations, 
6,500 feet 


Santa Margarita ? formation 
(middle Miocene),800 feet 


Vaqueros formation 
(lower Miocene), 820 feet 


Oligocene (?) 

Tejon formation 
(Eoeene),500 feet 


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Alluvium. 

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Light-colored sandstone and shale-pebble beds; 
locally gypsiferous clays 

Brownish sandstone and sandy shale 

Zone of Thais etchegoinensis,Peden coalingensis, etc. 

Lenticular beds of lignitic coal in Priest Valley 

( Massive blue sandstone beds 

Coarse brown sandstone and sandy shales 
Hard white volcanic ash 


Buff and gray massive sandstone varying to sandy 
shale; dark-gray clay shale, weathering chocolate- 
colored, at base 


Chocolate-colored to nearly white 
' diatomaceous and clay shales 

Coarse arkose sandstone, weathering to reef-like outcrops, sandy 
shale, resistant calcareous sandstone; locally conglomerate and 
carbonaceous shale, with coal near base 
Diatomaceous and foraminiferal shale; yellow gypsiferous 
and carbonaceous sandstones 

An additional 6,900 feet of upper Chico present east of 
Joaquin Rocks, north of Coalinga 


Thin-bedded dark clay shale and fine gray sandstone, 
massive sandstone, conglomerate, and pebbly sand¬ 
stone; coarse conglomerate at base 


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Thin-bedded gray shale with interbedded fine sand¬ 
stone, massive sandstone, and conglomerate; lower 
part grades into underlying conglomerates 


Lenticular conglomerate, similar to those above 
' and below; in places-very massive 


Thin-bedded dark-gray clay shale with thin beds 


of iron-gray quartzose sandstone 


Huge lenses of conglomerate, composed of pebbles of 
quartzite, dark-colored porphyries, granitic rocks, 
and schists in arkosic greenish-yellow sandstone 


Dark clay shale with small amounts of thin-bedded 
sandstone; contains Aucella sp. ? in lower 1,500 feet 


Fractured arkose, sandstone, black shale, varicolored chert, 
and locally different types of schist, with various 
intrusive rocks, mainly of a basic character 


5,000 FEET 


figure 3. Columnar section of rocks northeast of the San Andreas fault, central 

California. 




































































































































































































































































































OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 125 

the two are represented on the map and discussed together. Resting 
unconformably upon the Franciscan formation are dark clay shale, 
sandstone, and coarse conglomerate which represent both Lower and 
Upper Cretaceous. Eocene and Oligocene rocks are absent west of 
the Coalinga district, and the Vaqueros formation (lower Miocene) 
rests upon the Cretaceous or older rocks with marked unconformity. 
The Vaqueros formation is in turn overlain unconformably by a 
body of diatomaceous shale, whose equivalent was termed the Santa 
Margarita (?) formation 1 in the Coalinga report. For convenience, 
and also to show its equivalence to the shale in the region south of 
Coalinga, the same name is used here. The later Tertiary rocks, 
which overlie the Santa Margarita (?) formation with probable un¬ 
conformity, comprise a great mass of clay shale, brownish and bluish 
sandstone, and conglomerate. The lower part of this series of beds 
is the equivalent of the Jacalitos and Etchegoin formations, which 


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TERTIARY 

Tulare formation / 

(Pliocene), 150 to 200 feet / 


Upper and middle 
Miocene formations, 
3,100 to 3,300 feet 

— 

PRE- 

FRANCISCAN 

Granite and gneiss 

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Alluvium 

Light arkose sand and 
shale-pebble conglomerate 

Clay shale, sandy shale, and sandstone, 
with minor amounts of shale-pebble 
beds and chalky diatomaceous shale 


- 

Light-colored clay and diatomaceous shale 


5,000 FEET 
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Figure 4. —Columnar section of rocks southwest of the San Andreas fault, central 

California. 


occur along the foothills near Coalinga; the upper part, which is 
distinguished from the lower by its abundant pebbles of diatomaceous 
shale, is the equivalent of the Tulare formation (Pliocene) of the 
Coalinga district and the area farther east. 

In mapping the area between the San Andreas fault and the 
Coalinga district the formations younger than the Vaqueros and 
older than the Tulare were grouped into two divisions. The lower 
division embraces the diatomaceous shale that was described in the 
Coalinga report as the Santa Margarita (?) formation; and the upper 
division, which is termed the upper Miocene, comprises the Jacalitos 
and Etchegoin formations. The grouping of the formations into 
these map units has been adopted in order that the areal distribution 
of the diatomaceous shale might be shown, as it has a bearing on the 
possible occurrence of oil. 

In the area west of the San Andreas fault the diatomaceous shale 
is so irregularly distributed that no attempt has been made to show it 


1 U. S. Geol. Survey Bull. 398, p. 88, 1910. 






































126 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

separately on the map. It has therefore been grouped with the over- 
lying fossiliferous sands, which are regarded as the equivalent of the 
typical Santa Margarita and which are shown on the map as part 
of the upper Miocene. 

GRANITIC ROCKS. 

Granitic and associated schistose rocks are exposed in the western 
part of the region in small areas from which the overlying Tertiary 
beds have been eroded and along the San Andreas fault zone, where a 
small block of granite is faulted up against the late Tertiary. These 
rocks form part of a mass upon which the Tertiary beds rest in much 
or possibly all of the Salinas Valley. Granite rocks, evidently part 
of this same mass, outcrop in extensive areas in the Gabilan Range, 
whose south end lies about 10 miles west of Bitterwater Valley, and 
also in the Santa Lucia Range, on the west side of Salinas Valley. 
The granitic and associated schistose rocks in the Santa Lucia Range 
have been termed by Willis 1 the Coast complex. The age of the 
granite is not definitely known, but many geologists who have worked 
in the Coast Ranges believe that it is the equivalent of the granite in 
the Sierra Nevada and it is presumably of Jurassic age. In the area 
mapped the granite is in contact only with late Tertiary sedimentary 
beds which have been deposited upon it. 

JURASSIC (?) SYSTEM. 

FRANCISCAN FORMATION. 

The oldest sedimentary rocks in this part of the Diablo Range are 
those which occur in irregular areas in the central part of the range 
and which are mapped as the Franciscan formation. These rocks are 
of a variety of lithologic types, ranging from relatively little altered 
arkosic sandstone and shale to different kinds of schist, of which 
bluish glaucophane schist is prominent. Probably the type of rock 
that appears most abundantly is a very arkosic sandstone, much 
fractured and seamed with calcite. Small masses of gray limestone 
occur sparing^, but thin-bedded- reddish and greenish chert is 
abundant and weathers characteristically to prominent ragged out¬ 
crops. These sedimentary rocks are intruded by various igneous 
rocks, mainly of rather basic character, which are largely altered to 
serpentine, although locally the intrusive rocks are fairly fresh and 
unaltered. The relatively unaltered character of the rocks is par¬ 
ticularly noticeable near Hepsedam, where there is a considerable 
area of rather coarse textured, little altered granitoid rock, com¬ 
posed predominantly of hornblende and feldspar. The intrusive 
rocks, although clearly younger than the sedimentary beds and not a 


1 Willis, Bailey, Geol. Soc. America Bull., vol. 11, p. 419, 1900. 




OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 127 

part of the Franciscan, have been grouped with them in the mapping 
as the Franciscan formation. 

The granitic rocks and the Franciscan formation are nowhere in 
contact in this region and definite evidence regarding their relations 
can not be offered. Flowever, Fairbanks 1 has described the Fran¬ 
ciscan rocks as resting unconformably upon the eroded surface of the 
“ Coast complex ” at Slates Springs, on the west side of the Santa 
Lucia Range. As the various exposures of granite appearing about 
Salinas Valley are believed to be parts of one mass, the Franciscan 
rocks in the Diablo Range must be considered younger than the 
granite exposed west of the San Andreas fault. The Lower Creta¬ 
ceous (Shasta series) is evidently unconformable upon the Fran¬ 
ciscan. It shows fewer fractures and none of the results of meta- 
morphism which the Franciscan rocks exhibit, and in most of the 
region it may be differentiated readily from the older rocks. Along 
the San Andreas fault zone, however, the two formations are so frac¬ 
tured and intermingled that in the absence of fossils in the younger 
they appear to be indistinguishable. 

CRETACEOUS SYSTEM. 

Overlying the Franciscan formation unconformably is a succes¬ 
sion of beds of dark clay shale, arkosic sandstone, and conglomerate, 
which, in the area mapped, have an aggregate thickness of over 
19,000 feet. This succession of strata embraces .both the Shasta 
series (Lower Cretaceous) and the Chico formation (Upper Cre¬ 
taceous). Farther north, along the east flank of the Diablo Range, 
about 12 miles north of Coalinga, Cretaceous beds having a total 
thickness of at least 6,900 feet overlie the youngest Cretaceous beds 
exposed in the area shown on Plate V, giving a thickness of approxi¬ 
mately 25,900 feet for the Cretaceous section in the southern part 
of the Diablo Range. In many places the Cretaceous beds, espe¬ 
cially those belonging to the Shasta series, resemble somewhat the 
sedimentary beds in the Franciscan formation. The two terranes 
are evidently unconformable, however, for the Franciscan is much 
folded, faulted, and locally metamorphosed and is intruded by a 
multitude of igneous rocks, whereas even the lowest beds of the 
Shasta are much less fractured, are unmetamorphosed, and in this 
region are intruded by few if any igneous rocks. The unconformity 
between the youngest Cretaceous formation in this region and the 
oldest Tertiary in contact with it is clearly shown by the absence of 
many thousand feet of beds in- the Upper Cretaceous and early Ter¬ 
tiary which are exposed in hills north of Coalinga. 

1 Fairbanks, H. W., Stratigraphy at Slates Springs : Am. Geologist, vol. 18, pp. 350-353, 
1894. 




128 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

The Cretaceous section is best developed on the north side of 
Waltham Valley, where alternating beds of clay shale, arkosic sand¬ 
stone, and conglomerate of variable thickness form a northward¬ 
dipping monocline. In the report on the geology of the Coalinga 
district the Cretaceous rocks were described as embracing three divi¬ 
sions, an upper, middle, and lower, the last two of which are well 

developed in the region described in the present report. (See 

PI. V.) The line of separation between these two is the base of a 
massive conglomerate which outcrops near the crest of Juniper 

Ridge. The lower division, which is exposed southwest of that 

ridge, is about 14,900 feet thick. Although the lithologic changes 
in most of this division are so numerous both vertically and along the 
strike that it is difficult to separate it into well-defined members, it 
may for convenience be described as being composed of two parts. 
The lower part embraces about 3,500 feet of a dark-gray clay shale 
that weathers to light greenish gray, interstratified with sandy shale 
and numerous thin beds of fine-grained iron-gray quartzitic sand¬ 
stone. This part is best exposed southwest of Center Peak, where it 
rests, apparently in unfaulted contact, upon the Franciscan. 1 The 
upper part comprises about 11,400 feet of interstratified clay shale 
like that in the lower part, sandy shale, massive sandstone, and con¬ 
glomerate. The conglomerate, whose presence distinguishes the 
upper from the lower part of the division, is lenticular, in places 
reaching a thickness of about 1,200 feet and in places thinning and 
grading laterally into sandstone. The pebbles are well rounded and 
the largest measure about 8 inches in diameter. They are composed 
of quartzite, dark-colored porphyritic rock, and granitic rock 
and are embedded in a matrix of dark-greenish sandstone that 
weathers reddish brown. Between Waltham Valley and Los Gatos 
Creek the upper part of the lower division contains two prominent 
lenses of conglomerate. The lower lens, which has a maximum thick¬ 
ness of about 1,200 feet, forms the crest of Center Peak, from which 
it extends southeastward as a prominent ridge that trends nearly 
parallel to Juniper Ridge, on the west side of the canyon in which 
Fresno Hot Springs is situated. About 2,500 feet above this con¬ 
glomerate and separated from it by interstratified clay shale and sand¬ 
stone is another lens of coarse material which forms the ridge east of 
Fresno Hot Springs. Between this conglomerate and that which 
forms the base of the middle division are sandy shale and sandstone. 

The middle division includes the conglomerate exposed alonsr 
Juniper Ridge and a succession of clay shales and sandy shales that 

1 Owing to errors in the preparation of the map the Franciscan rocks in this area are 
shown as the Santa Margarita (?) formatiton, and in the geologic section on the map 
the two parts of the lower division of the Cretaceous system are termed the lower and 
middle divisions, and the middle division is termed the upper division. 



OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 129 


overlie it. In the report on the Coalinga district 1 the thickness of 
this division exposed on Alcalde Creek is given as 4,800 feet. This 
division of the Cretaceous is exposed also north of Coalinga, where, 
on the east flank of the Coalinga anticline northeast of the Joaquin 
Rocks, it is overlain by about 5,300 feet of massive concretionary 
sandstone and dark clay shale, upon which rest about 1,600 feet of 
shale filled with the remains of diatoms and foraminifers. These two 
last-mentioned members constitute what was described in the Coalinga 
report as the “ upper member of the Knoxville-Chico rocks.” 

About 1,500 feet above the base of the lower division were found 
abundant specimens of Aucella crassicollis (?), a fossil typical of 
the Lower Cretaceous. As there appears to be no marked lithologic 
or stratigraphic break in the lower 3,500 feet of the Cretaceous sec¬ 
tion—that is, up to the conglomerate that separates the two parts of 
the lower division—it seems probable that all of this part of the lower 
division is of Lower Cretaceous age. L T pper Cretaceous fossils have 
been found in the middle of the three divisions northeast of Juniper 
Ridge, and the conglomerate at the base of that division was de¬ 
scribed in the Coalinga report as the probable base of the Upper Cre¬ 
taceous. Only two fossils have yet been found in the upper part of 
the lower division. These, which were found near the top of the 
conglomerate that separates the two parts of the lower division, 
although not diagnostic, suggest Upper Cretaceous rather than Lower 
Cretaceous age, so that the line between the Shasta and Chico may 
occur at the base of the conglomerate that extends southeastward 
from Center Peak, instead of at the base of the conglomerate that 
appears at the base of the upper division along Juniper Ridge, as 
was suggested in the report on the Coalinga district. 1 

The Cretaceous near Jacalitos Creek and along the San Andreas 
fault zone consists largely of dark clay shale of Lower Cretaceous 
age, in which Aucella crassicollis (?) is fairly abundant. Only a few 
of the areas of Cretaceous that occur along the south side of Waltham 
and Lewis creeks have been shown, many small areas having been 
grouped in the mapping with the Franciscan. 

LTpper Cretaceous rocks are unknown south of Waltham Valley 
within the boundary of the area shown on Plate V. Rocks of that age 
occur, however, in a small area at the crest of the Diablo Range about 
a mile north of the Stone Canyon coal mine. 

TERTIARY SYSTEM. 

EOCENE AND OLIGOCENE ( ?) SERIES. 

Early Tertiary rocks are but sparingly represented in the area 
mapped, outcropping only in a narrow belt some 3 miles in length 

1 Arnold, Ralph, and Anderson, Robert, Geology and oil resources of the Coalinga dis¬ 
trict : U. S. Geol. Survey Bull. 398, p. 53, 1910. 





130 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

in the foothills west of Coalinga. Near the San Joaquin Valley coal 
mine these beds, which were mapped as the Tejon formation in the 
report on the Coalinga district 1 but which include probable Oligo- 
cene as well as true Tejon, rest unconformably upon the Cretaceous 
and are overlain unconformably by the Vaqueros formation. The 
beds consist of about 200 feet of whitish gypsiferous and carbona¬ 
ceous Eocene sandstone (the true Tejon) overlain by white diatoma- 
ceous and foraminiferal shale of probable Oligocene age. These 
beds outcrop for many miles to the north in the foothills bordering 
San Joaquin Valley, where the shale is at least 1,000 feet thick. 
They also continue to the south, probably underlying much of the 
area w r here late Tertiary rocks appear at the surface south of Coa¬ 
linga, and outcrop along the flank of Reef Ridge, southeast of the 
area shown on the map (PI. V). The Oligocene (?) diatomaceous 
shale overlying the Tejon formation (Eocene) is of economic im¬ 
portance, as it is probably the ultimate source of most of the petro¬ 
leum in the Coalinga field. 

MIOCENE SERIES. 

VAQUEROS FORMATION (LOWER MIOCENE). 

The oldest Tertiary formation that has any considerable areal dis¬ 
tribution in the region mapped is the Vaqueros formation, which is 
composed mainly of massive sandstone that contains a good marine 
fauna of lower Miocene age. It outcrops in the foothills west of 
Coalinga; in irregular areas in the mountainous part of the range, 
mainly south of Waltham and Priest valleys; and in a narrow 
belt, about a mile in length, northeast of Priest Valley. It doubt¬ 
less occurs also beneath the later Tertiary formations in parts of 
Waltham and Priest valleys, but its extent there is a matter of con¬ 
jecture. Lower Miocene rocks do not outcrop west of the San 
Andreas fault within the area shown on Plate V. The Vaqueros 
occurs, however, in a narrow fault block within the San Andreas 
fault zone southwest of the Stone Canyon mine, and farther south¬ 
east in the Parkfield region it is reported by Eldridge 2 on the south¬ 
west side of the fault zone. 

In the foothills west of Coalinga this formation overlaps uncon¬ 
formably the Oligocene (?) diatomaceous shale, and elsewhere in 
the area mapped it rests with marked unconformity upon either the 
Franciscan or the Cretaceous rocks. Resting unconformably upon 
the Vaqueros is a body of diatomaceous shale that is mapped as the 
Santa Margarita (?) formation. The unconformity between these 
formations is well shown in the central part of the range by the 
irregular way in which the Santa Margarita (?) overlaps the Va- 


1 U. S. Geol. Survey Bull. 398, pp. 62-75, 1910'. 

2 Eldridge, G. H., unpublished notes. 



OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 131 

queros. The relationship is most clearly shown on the west side of 
Deep Well Canyon, where the two formations show a discordance in 
dip of over 20° and the basal sandstone of the Santa Margarita (?) 
lies on the eroded edges of the Vaqueros. The unconformity is 
also indicated in the syncline north of Smith Mountain, where the 
line along which the Vaqueros is folded is offset from that along 
which the Santa Margarita (?) is folded. 

Neither the lithology nor the thickness of the Vaqueros is con¬ 
stant, and although the variation in thickness is partly due to ero¬ 
sion subsequent to deposition and the removal of the upper part of 
the formation, it is also partly due to the fact that the formation 
was laid dow r n upon a very irregular surface and that in consequence 
the lowest beds were not everywhere deposited. 

The Vaqueros is probably most completely exposed near the crest 
of the range southeast of Smith Mountain, where it has a thickness 
of about 820 feet. The lower 200 feet or so is composed of car¬ 
bonaceous shale, containing beds of coal and a conglomerate and 
coarse sandstone, made up largely of fragments of Franciscan rocks. 
Above this is about 220 feet of very resistant calcareous sandstone 
that forms the crest of the castellated ridge of which Smith Moun¬ 
tain and Smith Pinnacles are parts. Overlying the calcareous sand¬ 
stone and forming the upper part of the Vaqueros are about 400 feet 
of alternating hard and soft sandstones. The more resistant beds 
weather out prominently and in places where the overlying softer 
beds have been stripped off form broad, bare dip slopes 400 feet or 
more in length. The presence of such resistant reef-like beds as 
these is one of the most characteristic features of the Vaqueros in 
the southern part of the Diablo Range. 

On Lewis Creek the Vaqueros contains a considerable amount of 
pinkish shale, probably diatomaceous, which is similar to that in the 
overlying Santa Margarita (?), and the two formations are sepa¬ 
rable with difficulty. 

SANTA MARGARITA(?) FORMATION (MIDDLE MIOCENE). 

Resting unconformably on the Vaqueros is a formation composed 
of TOO to 800 feet of purplish to gray diatomaceous and clay shale 
which weathers to pinkish-white or chocolate-colored outcrops. 
This formation is practically continuous in outcrop and varies little 
in lithology from the north side of Lewis Creek to the southeast 
corner of the area shown on the map and for about 2o miles farther 
south along Reef Ridge. In the report on the geology and oil re¬ 
sources of the Coalinga region this shale was described as the prob¬ 
able equivalent of the Santa Margarita formation. In order to show 
its equivalence to the shale south of Coalinga, the name Santa Mar¬ 
garita^) is used in the present discussion. 

62083°—14-2 



132 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1013, PART II. 

Where the Santa Margarita (?) is best exposed the lower 15 to 40 
feet is a massive arkosic sandstone lithologically like that in the 
Vaqueros formation. Above this lower sandstone is from 200 to 800 
feet of hard and brittle diatomaceous clay shale which breaks with 
a splintery fracture and weathers pink or nearly white. The shale 
forms little or no soil and weathers to steep ridges and knobs which 
are recognizable at considerable distances by their chalky-white or 
pinkish color and by the light growth of pine and manzanita which 
they support. Toward the top the shale gradually becomes more 
clayey and grades into a dark-gray clay shale which weathers to 
platy chocolate-colored fragments and forms a cla^y soil. This 
change does not seem to take place along an exact stratigraphic line, 
but from place to place one facies increases in thickness at the expense 
of the other. No evidence of unconformity between the diatomaceous 
shale of the Santa Margarita (?) formation and the sandy beds of 
the upper Miocene was found, the line of contact being drawn at the 
horizon where the shale becomes sandy rather than clayey and 
weathers yellowish brown rather than purplish. 

UPPER MIOCENE FORMATIONS. 

Distribution and character .—Numerous beds of sandstone, con¬ 
glomerate, and diatomaceous and clay shale that were deposited 
during the later part of the Miocene have been grouped together 
in the mapping as “ chiefly upper Miocene.” These beds occur on 
both the northeast and southwest sides of the San Andreas fault, 
but they are not precisely the same in character nor exactly equiva¬ 
lent stratigraphically in the two areas. Most if not all of the rocks 
thus mapped southwest of the fault are regarded as the equivalent 
of the Santa Margarita formation and therefore as of middle 
Miocene age. Those northeast of the fault constitute the westward 
continuation of the Jaealitos and Etchegoin formations (upper 
Miocene) in the Coalinga region and, in the lower part, embrace some 
beds of probable Santa Margarita (middle Miocene) age. The 
reasons for grouping the formations in this manner in the geologic 
mapping is explained in the general statement about the geology. 
(See p. 125.) The Jaealitos and Etchegoin formations are believed 
to be in the main younger than the true Santa Margarita, although 
the fauna contained in the lower part of what is mapped as upper 
Miocene in Waltham Canyon shows a close similarity to that of the 
true Santa Margarita. It should also be noted that the diatomaceous 
shale in the lower part of the beds mapped as upper Miocene west 
of the fault may be the correlative of the shale mapped as the Santa 
Margarita (?) formation east of the fault. A full discussion of the 
possible relationship of these formations can not be given here nor 
can a decision be reached until careful paleontologic study is made. 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL.. 133 

Area southwest of the San Andreas fault. —Between the San An¬ 
dreas fault and Salinas River the granite is overlain by beds of shale 
and sandstone, which contain marine fossils characteristic of the 
Santa Margarita formation and which in the area mapped have a 
maximum thickness of about 3,300 feet. Near Lonoak the lower 
800 to 1,000 feet is composed largely of diatomaceous and clay shale 
which weathers to a light-pink or chocolate color and which contains 
relatively little interstratified sand, although the lower part is in 
some places somewhat sandy and in a few places, as at the asphalt 
quarry west of Lonoak, is a coarse arkosic grit. This shale resembles 
closely the “ chalky ” shale of the Monterey group. It was described 
as Monterey shale by Eldridge, 1 but as the writers discovered in it 
fossils that are believed to be characteristic of the Santa Margarita 
formation, they have grouped it in the present report with the over- 
lying more sandy beds. Shale of this type has a somewhat local dis¬ 
tribution in the area mapped, apparently grading along the strike 
into sandy shale and sandstone. Overlying the diatomaceous shale 
near Lonoak is about 1,100 feet of sandy shale, above which is about 
1,200 feet of sandy shale and fine-grained clayey sandstone con¬ 
taining thin beds of diatomaceous shale and of conglomeratic sand¬ 
stone filled with pebbles of white flinty shale. The interbedded shale 
in the upper 1,200 feet is very light colored and “chalky” and is 
perhaps partly volcanic ash. Although occurring in beds only a few 
feet thick, interstratified with sandstone, it is almost free from 
coarse material. Marine fossils are abundant in the upper part of 
the formation, the large barnacle Tamiosoma gregaria being excep¬ 
tionally common in the uppermost 1,000 feet. 

Area northeast of the San Andreas fault. —Northeast of the San 
Andreas fault is a succession of beds of sandstone, sandy shale, and 
conglomerate, which in the hills w T est of Coalinga is separated into 
the Jacalitos and Etchegoin formations but which in the rest of the 
area is mapped with the upper Miocene. These beds rest upon the 
diatomaceous shale of the Santa Margarita (?) formation, into which 
they seem to grade, and the line of separation has been drawn arbi- 
trarily so that the predominantly shaly beds are included in the 
Santa Margarita (?) and the predominantly sandy beds in the upper 
Miocene. The line between the upper Miocene and the Tulare for¬ 
mation (Pliocene) is only a little more definite and has been drawn 
at the base of the beds which contain abundant pebbles of diatoma¬ 
ceous shale. 

In the upper part of Waltham Valley the upper Miocene beds have 
a maximum thickness of about 6,500 feet. The lower 500 to 600 
feet is mainly sandy shale that weathers yellow or brown and shaly 

1 Eldridge, G. H.. The asphalt and bituminous rock deposits of the United States: IT. S, 
Geol. Survey Twenty-second Ann. Rept., pt. 1, p. 408, 1901. 




134 CONTRIBUTIONS TO ECONOMIC GEOLOGY , 1913, PART II. 

sandstone, above which is about 2,800 feet of buff, brown, and 
greenish-yellow sandstone and shaty sandstone with a little coarse 
grit and conglomerate. Thin beds of white ash occur at irregular 
intervals in the upper 1,000 feet of this member, the most prominent 
being a bed 10 to 20 feet thick that occurs about 2,700 feet above the 
top of the Santa Margarita (?) formation. The buff sandstone 
grades upward into beds, less than 600 feet thick, of massive coarse¬ 
grained white and blue sandstone interbedded with fine sandstone. 
Above the blue sandstone is about 900 feet of brown sandstone and 
sandy and carbonaceous shales. In Priest Yalley the upper 425 feet 
of this member contains lignitic sandy brown shale, in which occur 
beds of low-grade coal that have been prospected at a few places. 
Above the carbonaceous beds massive gray and buff sandstone and 
clayey sands alternate for 1,500 feet up to the beds containing shale 
pebbles, which form the base of the Tulare. 

TULARE FORMATION (PLIOCENE). 

The youngest formation in this region that has suffered marked 
deformation is composed of beds of rather poorly consolidated sand¬ 
stone, shale, and conglomerate, which were deposited either in lakes 
or subaerially. On account of similarity in lithologic character and 
in stratigraphic position this formation is correlated with the Tulare 
formation, which is typically exposed in the Coalinga region. In at 
least part of the Priest Valley region it lies unconformably upon the 
underlying upper Miocene formations just described, and throughout 
the region it is overlain with marked unconformity by the flat-lying 
Quaternary deposits. Beds correlated Avith the Tulare are exposed in 
three general areas—(1) in the Priest Valley syncline, (2) along the 
San Andreas fault zone, and (3) on the foothills west of Peachtree 
Valley, in the center of the Peachtree syncline, and northwest of the 
area mapped. 

In the southern part of Salinas Valley is the Paso Robles for¬ 
mation, which consists in part of fresh-water beds similar in litho¬ 
logic character to the Tulare and probably of the same age, but work 
done near the type locality by Robert Anderson indicates that there 
is a lower marine member of the Paso Robles, which is the repre¬ 
sentative of the Etchegoin formation of the Coalinga region, and for 
this reason the name Tulare is used for the purely fresh-water beds 
of the Priest Valley and neighboring regions. 

The lithology and thickness of the Tulare varies considerably in 
the different areas. In the Priest Valley syncline it comprises not 
less than 500 to 600 feet of incoherent light-colored, poorly sorted 
angular, distinctly arkosic sandstone and conglomerate. Pebbles 
of diatomaceous shale like that in the Santa Margarita (?) formation 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 135 

northeast of the San Andreas fault and in the Monterey group west 
of the Salinas Valley are very common in the conglomerate. These 
beds weather to light-gray outcrops that contrast markedly with the 
brownish color that is characteristic of the upper Miocene. There is 
no sharp change in lithology between the upper Miocene and the 
Tulare, and the line of contact has been drawn at the base of the 
beds which contain abundant pebbles of diatomaceous shale. This 
gradual change in lithology and the lack of any structural evidence 
of interrupted sedimentation suggest that the formations are con¬ 
formable here. Also in much of Waltham and Priest valleys a 
fossiliferous zone containing characteristically Pecten coalingensis , 
Pecten wattsi , and Thais etchegoinensis occurs at about the same 
stratigraphic distance below the base of the Tulare, suggesting that 
an unconformity, if present, does not represent an important interval 
of erosion. 

In the San Andreas fault zone the Tulare formation is composed 
of coarse arkose and shale pebble beds like those described above 
and in addition contains red and green clays, in which there are 
numerous beds of gypsum. The unconformity between the Tulare 
and the upper Miocene formations is shown by the presence of a con¬ 
glomerate near Alvarez Creek containing numerous bowlders of 
fossiliferous sandstone of upper Miocene age, the equivalent of the 
Jacalitos or Etchegoin formation. Southwest of the San Andreas 
fault the Tulare comprises a basal bed some 10 to 15 feet thick of 
indurated shale-pebble conglomerate, above which are incoherent 
gray sand and sandy clay, the total thickness being not over 150 or 
200 feet. 

QUATERNARY SYSTEM. 

In Quaternary time the Priest Valley region was an area of erosion 
rather than of deposition, and it therefore contains no large Quater¬ 
nary deposits. The beds of the larger streams are covered with allu¬ 
vium, but this material is only a temporary deposit, formed in the 
course of its transportation beyond the area here described. South¬ 
west of the San Andreas fault alluvium seems to be collecting in the 
stream beds, and the alluvial deposits on the valley floors are rela¬ 
tively greater in that area than in the area northeast of the fault. 

0 

STRUCTURE. 

The dominant structural feature in this part of the Diablo Range 
is the San Andreas fault, which trends diagonally across the region 
mapped, separating it into two parts, which exhibit two distinct 
types of structure. The dissimilarity in the stratigraphic record on 
opposite sides of the fault, or fault zone, as it might more properly 
be termed, shows that pronounced movements have taken place along 


136 CONTRIBUTIONS TO ECONOMIC UEOLOG1, l l Jl3, BART li. 

it since at least as far back as middle Miocene time. The move¬ 
ments along the line farther north, which caused the earthquake of 
April 18, 1906, were almost wholly horizontal, but the lack of the 
Franciscan, the Cretaceous, and the Vaqueros formation and the 
presence of granite at or close to the surface in the area west of the 
fault seem to indicate that there was once very considerable vertical 
movement along this general zone, the net result of which was an 
elevation of the mass lying west of the fault relative to that lying 
east of it. The fault zone varies in width from half a mile to a mile 
and is composed of a number of approximately parallel fractures, 
which separate long blocks of the various formations. The line 
shown on the map as the San Andreas fault is the fracture along 
which movement seems to have taken place most recently and which 
may be considered the active fault. This line is marked by numerous 
small sunken areas, some of which are occupied by lakes throughout 
the year and which are especially notable along the flat summit of 
Mustang Ridge. 

In the area west of the fault the granite has evidently furnished 
a foundation sufficiently rigid to prevent more than a minor amount 
of warping, and the Tertiary beds a short distance west of the fault 
zone are rarely tilted over 10° and in most places less than 5°, form¬ 
ing short and for the most part irregular folds or domes. The only 
large fold in this part of the region is the broad, shallow Peachtree 
syncline, which extends northwestward from a point near the center 
of the Peachtree ranch for more than 10 miles beyond the boundary 
of the area shown on the map. The dips on either flank of this fold 
are so low through most of its course that the precise location of its 
axis is hard to determine. The dip on both flanks is slightly irregu¬ 
lar, and at one place in Bitterwater Valley, just below the mouth of 
Lewis Creek, a low dip toward the east forms a very short subsidiary 
anticline in the east flank of the larger syncline. 

In the mountainous part of the range northeast of the fault zone 
the rocks are bent into a multitude of folds and are broken by faults, 
most of which trend approximately parallel to the San Andreas 
fault and somewhat obliquely to the course of the Diablo Range. 
The largest of these folds is the syncline which forms Priest Valley 
and which extends from it southeastward through the upper part of 
Waltham Valley. This general synclinal structure continues, 
although not exactly as an unbroken syncline, farther southeastward 
past Curry Mountain and merges into the monoclinal structure 
along the flank of Reef Ridge. In this structural trough Tertiary 
beds which aggregate in thickness about 8,500 feet have been in¬ 
folded. On the south the basin is bounded by the mass of Franciscan 
rocks that, with various infolded and faulted bodies of Cretaceous 
and Tertiary rocks, forms the ridge on the south side of Waltham 


OIL PROSPECTS IX WALTHAM 


AND OTHER VALLEYS, CAL. 


137 


and Priest valleys. On the north side of the basin the Tertiary 
formations abut against the northward-dipping monocline of Cre¬ 
taceous rocks. Although the folding is pronounced and the Ter¬ 
tiary beds are in places tilted on edge or are even overturned, yet the 
forces causing the deformation seem to have spent themselves in a 
relatively narrow zone and did not greatly affect the Cretaceous 
beds that lie 1^ to 2 miles from the axis of folding. These Cretaceous 
beds were evidently tilted before middle Miocene time to approxi¬ 
mately their present attitude, as is shown by the fact that in small 
areas north of Priest Valley and near Alcalde Canyon almost flat 
Tertiary beds rest upon the steeply dipping Cretaceous rocks. The 
difference in the character of the foundation upon which the upper 
Miocene formations rest in the north and south sides of Waltham 
and Priest valleys suggests that the fold in the Tertiary beds follows 
an old line of weakness along which the Cretaceous beds were faulted 
against the Franciscan in pre-middle Miocene time. Between the 
center of the synclinal basin and the San Andreas fault are numerous 
areas of Tertiary rocks flexed into short, shallow folds. The syn¬ 
clines are for the most part unbroken, but the anticlines are almost 
invariably faulted and a narrow belt of Franciscan rocks is exposed. 

The complexity of the structure gradually diminishes toward the 
east, and in the foothills bordering the San Joaquin Valley the Ter¬ 
tiary rocks which appear at the surface form only a few broad folds. 
In the area shown on the map only the part lying east of Curry 
Mountain may be said to belong to this foothill belt. 

PETROLEUM. 


CONDITIONS IN THE COALINGA DISTRICT. 

The area discussed in this report lies mainly in the mountainous 
region west of the Coalinga oil field, one of the largest producing 
fields in California, and a discussion of the possibility of developing 
oil in it may well be preceded by a brief account of the occurrence 
of oil in the productive field. 1 

The oil sands in the Coalinga district lie in the midst of a thick 
mass of sedimentary beds, mainly of marine origin and of Cretaceous 
and Tertiary age. These beds are mostly sandstone and clay or 
clay shale, but they include two persistent formations which are 
filled with the remains of minute organisms—diatoms and for- 
aminifers—and which are commonly termed diatomaceous shales. 
One of these formations lies at the top of the Cretaceous and the 
other in the lower part of the Tertiary, and in much of the region 
the two are separated by many hundred feet of sandstone and shale. 
With one exception the oil-bearing sands may be grouped in two 


i For a full discussion of the Coalinga district see T T . S. Geol. Survey Bull. 398, 1910. 





138 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

zones, one including the sandy beds immediately overlying, under¬ 
lying, and intercalated with the lower (Cretaceous) shale, the other 
comprising the sands that have a similar relation to the upper 
(Tertiary) diatomaceous shale. The single exception to this group¬ 
ing is an oil sand which occurs in the sandstones and shales and 
which lies between the two diatomaceous shale formations but is 
separated from each of those formations by several hundred feet of 
barren strata. The upper of the two main zones is by far the more 
productive, and from the sands overlying the Tertiary diatomaceous 
shale comes more than 99 per cent of all the oil produced in the 
Coalinga district. The close association of oil-bearing sands and 
diatomaceous shales is not unique in the Coalinga region but is the 
one practically constant feature that may be recognized in all the 
productive oil fields in the southern half of California. This con¬ 
stant relation has led to the belief that most if not all of the 
petroleum in the southern half of the State had its origin in the 
diatomaceous shales. The sandstones in contact with the diato¬ 
maceous shales are not everywhere petroliferous; they contain oil in 
quantity only in places where structural and other conditions have 
caused it to accumulate. In the Coalinga district the main accumu¬ 
lations lie along a broad anticlinal fold that extends southeastward 
from the Diablo Range, forming an outlying range of hills east 
of the town of Coalinga, and also at the upper end of the plunging 
syncline that lies between the anticline and the main range. In 
general it may be said that structures of this type appear to govern 
the occurrence of petroleum in most of the productive fields in the 
southern half of California. Petroleum is usually found in the 
anticlinal folds, but in many places, especially along the west side 
of San Joaquin Valley, oil occurs also in the synclines that parallel 
anticlines in which the sands are saturated with petroleum. 

With this general idea of the manner in which oil occurs at Coa¬ 
linga in mind the broader features of the region west of Coalinga 
will be considered to show how far the conditions existing at Coa¬ 
linga are duplicated. 

CONDITIONS IN WALTHAM, PRIEST, BITTERWATER, AND 

PEACHTREE VALLEYS. 

The San Andreas fault divides the region west of Coalinga into 
two parts, whose structure is so diverse that they may best be treated 
separately even in this general discussion. 

In the mountainous region between the San Andreas fault on the 
west and the Coalinga district on the east neither of the diatomaceous 
shale formations with which the oil sands of the Coalinga district are 
associated occurs. There is present, however, a younger formation 
of precisely the same type, in which oil might have been formed 
equally as well as in either of the older shales at Coalinga. Indeed. 


OIL PROSPECTS LN WALTHAM AND OTHER VALLEYS, UAL. 139 

this shale, which is shown on the map as the Santa Margarita (?) for¬ 
mation, continues southeast and forms part of the huge body of shale 
trom which the oil obtained in the Temblor Range fields is believed, 
to have been derived. The structure in the mountainous region west 
of Coalinga is, however, very unlike that in the foothills, and the 
Tertiary rocks, instead of being folded into broad anticlines and 
synclines as they are along the eastern margin of the Diablo Range, 
are sharply flexed and faulted and occur in more or less isolated 
blocks resting on the older formations. Thus the structure is in 
general not favorable for the collection of oil that may have been 
derived from the diatomaceous shale, and a duplication of the condi¬ 
tions existing in the Coalinga field is not to be expected. There is a 
slight chance that oil may have collected beneath a small area lying 
south of Curry Mountain, but it seems improbable that much oil has 
concentrated there. Besides the diatomaceous shale there is in this 
part of the region another mass of sedimentary rocks that must be 
considered a possible source of petroleum. This mass comprises the 
dark-colored compact clay shale containing traces of carbonaceous 
matter that lies in the lower part of the Cretaceous and is especially 
well exposed on the north side of the upper part of Waltham Valley. 
This dark clay shale is very like the shale in Colusa and Glenn 
counties, in northern California, in which seeps of oil occur. How¬ 
ever, throughout the region the Cretaceous shale is steeply tiltled and 
nowhere has an attitude favorable for the collection of petroleum. 

In the foothills west of the San Andreas fault the lower part of the 
Tertiary formation contains masses of diatomaceous shale that reach 
thicknesses of several hundred feet. Asphalt and dry oil sand occur 
associated with the shale, and this area of low dip should be critically 
examined as one in which petroleum might have accumulated. 

LOCAL AREAS. 

AREA SOUTH OF CURRY' MOUNTAIN. 

GEOLOGY AND ECONOMIC POSSIBILITIES. 

In the area of relatively low relief near the southeast corner of 
T. 21 S., R. 14 E., between the upper part of Jacalitos Creek and 
Curry Mountain, several structures merge, and, although the domi¬ 
nant feature is the general synclinal structure that produces Wal¬ 
tham Valley, the rocks are folded into a number of small irregular 
anticlines and svnclines. The beds appearing at the surface are of 
late Miocene age. The older Tertiary beds, which were mapped in the 
Coalinga report 1 as the Santa Margarita (?), Vaqueros, and Tejon 
formations, appear to the southeast along Reef Ridge; but to the 
northwest, about Curry Mountain, the later Miocene strata rest di¬ 
rectly upon the Cretaceous, and the older Tertiary formations are not 


1 U. S. Geol. Survey Bull. 398, 1910. 



140 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

exposed anywhere between that place and Alcalde Canyon. The oil 
obtained in the mam Coalinga field is believed to have originated in 
the diatomaceous shale which in the Coalinga report was mapped as 
the upper part of the Tejon formation but has since been proved 
to be younger than Tejon and probably of Oligocene age and to have 
migrated from that shale into the sandstones that immediately 
underlie, overlie, or are bedded with it. The most prolific oil sands 
are those immediately above this diatomaceous shale, and in general 
the sands become less productive the farther they are removed from 
it. Moreover, the seeps of oil that occur farther south, along Reef 
Ridge, bear a similar relation to the diatomaceous Oligocene (?) 
shale. 

The absence of outcrops of the Oligocene ( ?) shale and the Tejon 
formation (Eocene) in the area south of Curry Mountain is there¬ 
fore of prime importance in considering the possible occurrence of 
oil in this part of the region. The southernmost exposure of this 
shale and of the Tejon formation north of Alcalde Canyon is near 
the San Joaquin Valley coal mine 3 miles due west of Coalinga. 
From that place to Sulphur Canyon, 10 miles almost due south of 
Coalinga and about 3 miles east of the southeast corner of the area 
mapped, the Oligocene (?) shale and the Tejon are covered by 
younger formations. The western boundary of the shale and the 
Tejon beneath the mantle of younger formations is of course not 
known, but as they do not outcrop in the western end of Reef Ridge 
it seems probable that the Eocene-Cretaceous contact has a general 
northwest-southeast trend parallel to the structure lines in the outer 
foothills south of Coalinga, and that the Oligocene (?) shale and the 
Tejon do not extend far, if at all, west of the axis of the Jacalitos 
syncline. The Vaqueros and Santa Margarita (?) formations like¬ 
wise are covered by the later Tertiary strata, but as they are exposed 
along the south side of upper Jacalitos Creek it is evident that both 
of these formations extend somewhat farther west than the Tejon 
and the Oligocene (?) shale. An attempt has been made in the dia¬ 
grammatic section (fig. 5) to show the probable attitude and rela¬ 
tionship of the Tertiary formations in the area southeast of Curry 
Mountain. The Oligocene (?) shale and Tejon formation are shown 
extending a short distance west of the axis of the Jacalitos syncline, 
where they are overlapped by the unconformably overlying Vaqueros 
formation. From this point they are continuous eastward and prob¬ 
ably underlie much of the broad Kettleman Plain. It is believed that 
petroleum has originated here, as it has in the Coalinga field to the 
north, in the diatomaceous Oligocene (?) shale that overlies the 
Eocene Tejon formation and has migrated into the overlying 
Vaqueros to places where the structure is favorable for its retention. 
It was pointed out in the Coalinga report 1 that the Jacalitos anti- 


1 V. S. Oeol. Survey Bull. 398. pp. 238. 239, 1910. 




OIL PKOSPECXS IN WALTHAM AND OXHEli VALLEYS, CAL. 141 


cline is a favorable place for the collection of such oil. Since that 
report was written wells drilled along this fold have obtained some 
light-gravity oil, apparently 
from the Yaqueros formation, 
at depths of 3,700 to 4,400 feet. 

The question now arises 
whether or not sufficient oil is 
present to saturate not only 
the sands along the Jacalitos 
anticline but also those on the 
west side of the Jacalitos syn¬ 
cline in a manner analogous to 
the occurrence of oil in both 
the Coalinga anticline and svn- 
cline. 

The general conditions in 
this area south of Curry 
Mountain are similar to those 
in sec. 2, T. 21 S., R. 14 E., a 
mile or so west of the Westside 
Coalinga field, where the Ya¬ 
queros formation rests directly 
upon Cretaceous beds. Wells 
drilled in this northern region 
obtain oil at a shallow depth 
from beds in the lower part of 
the Yaqueros. The conditions 
in sec. 2 are shown diagram- 
matically in figure 6. 

The oil obtained in the wells 
in and near sec. 2 probably 
had its origin largely in the 
Oligocene (?) shale, migrated 
into the Yaqueros and thence 
to the west up the dip, to accu¬ 
mulate finally in the area 
where the Yaqueros is but 
si i ght ly tilted. Although 
there is thus a general simi¬ 
larity between the structure of 
the area south of Curry Moun¬ 
tain and that of the area above 
mentioned, north of Alcalde 
Canyon, it appears rather unlikely that oil has migrated in quantity 
west of the axis of the Jacalitos syncline to collect in the irregu- 







































142 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, FART II. 

larly folded rocks south of Curry Mountain. The Oligocene (?) 
shale evidently lies much farther east in this area than in the area in 
sec. 2 north of Alcalde Canyon, and the Jacalitos anticline, along 
which oil rising from beneath the valley to the east would probably 
lend to collect, is interposed between the area of low dip near Curry 
Mountain and most or possibly all of this shale. More direct evidence 
on this point is the fact that the outcrops of the sands in the lower 
part of the later Miocene formations, where they are in contact 
with the Cretaceous on the southeast slope of Curry Mountain, show 
no trace of oil, whereas the outcrops of the Miocene sands from which 
the wells in sec. 2, T. 21 S., R. 14 E., derive oil do show such traces. 
The wells that have been drilled along the Jacalitos anticline. 

ui 

2 

jw of 

•2f cJ 

a > — 



Figure 6. —Hypothetical cross section in the western part of the Coalinga oil field, Cal. 

Adapted from U. S. Geol. Survey Bull. 398, fig. 8, p. 191, 1910. 

although they prove the presence of oil, have not yet shown that it 
occurs in great quantities. Unless the sands along the anticline are 
saturated with oil it is improbable that they will contain it farther 
west. Thus any prospecting in the area south of Curry Mountain 
should await further work along the anticline to the east. 

Two formations other than the Oligocene (?) shale might be re¬ 
garded as possible original sources of oil in the Jacalitos Hills—one 
the shale that occurs at the top of the Cretaceous in the north end 
of the Coalinga field and the other the shale of the Santa Margarita 
(?) formation. It is unlikely, however, that much if any oil which 
may have formed in either of these shales has collected in the 
Tertiary beds at the south end of Curry Mountain. The nearest 
exposures of the Cretaceous shale are in the north end of the Coalinga 














OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 143 

field. This shale is not exposed south of Coalinga, and in all proba¬ 
bility if it underlies the Jacalitos Hills at all it is much farther east 
than the Oligocene ( ?) shale and is therefore a much less likely 
source than that formation. As for the shale of the Santa Margarita 
(?) it should be noted that where it is exposed on Jacalitos Creek, 
at the north end of Reef Ridge, that formation is not more than 300 
or 400 feet thick. Moreover, this formation evidently decreases in 
thickness toward the north, beneath the cover of the younger forma¬ 
tions, and it is not exposed in the steeply tilted monocline of late 
Tertiary formations in the foothills north of Coalinga. 

WELLS DRILLED FOR OIL. 

Wells drilled along the Jacalitos anticline by the Bohemian Oil 
Co. and the Hub Oil Co. are said to have found oil sands at depths 
of about 3,700 and 4,300 feet, respectively. Farther southeast along 
the same fold the well of the Azores Oil Co. is said to have obtained 
oil at 3,500 feet. In the Jacalitos syncline to the west several wells 
have been drilled, but so far as the writers are aware none of them 
penetrated the strata of the later Tertiary formation and reached the 
horizons at which oil sands, if they exist in the region, might be 
expected to occur. 

About 13 or 14 years ago three wells were drilled along the upper 
part of Jacalitos Creek. Two were put down by the Whale Oil Co. 
in the SE. J sec. 4, T. 22 S., R. 14 E., one to a depth of 650, the 
other 600 feet. Salt water was obtained in the deeper well. Near the 
south line of sec. 32, T. 21 S., R. 14 E., the Venus Oil Co. drilled a 
well about 1,500 feet deep without obtaining oil. These three wells 
could hardly have been drilled in more disadvantageous places, for 
the Tertiary beds are steeply tilted and faulted, offering no favorable 
structure for the concentration of oil should it have occurred dis¬ 
seminated through the strata. 

WALTHAM AND PRIEST VALLEYS. 

The Tertiary formations in Waltham and Priest valleys lie in a 
structural depression that trends diagonally across the Diablo Range. 
The structure, though in general synclinal, is complicated, especially 
on the southwest, by numerous small folds and faults that have in¬ 
folded or dropped blocks of the Tertiary beds into the Franciscan. 
This structure is not specially favorable for collecting any petroleum 
that may have occurred in small quantities throughout the rocks, nor 
are there here any large areas underlain by diatomaceous shale from 
which oil might be derived. The diatomaceous shale of the Santa 
Margarita (?) formation has at best relatively small distribution, 
even though it underlie most of the region where the later Miocene 
formations appear at the surface. The tremendously thick section 


144 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

of dark carbonaceous shale that forms the lower part of the Cre¬ 
taceous on the north side of Waltham Valley might be regarded as 
an original source of petroleum, but its high and regular dips afford 
no favorable structure for the accumulation of oil, even if it were 
originally present. 

Indications of oil have been reported near the northwest corner of 
sec. 28, T. 20 S., R. 13 E., along the fault that extends northwest- 
southeast through the hills on the north side of Waltham Valley, 
about a mile west of Fresno Hot Springs. The writers were unable 
to confirm this report but are inclined to credit it. Such oil may 
have risen either from the dark carbonaceous shale of the Cretaceous 
or from the diatomaceous shale of the Santa Margarita (?), which 
supposedly lies beneath the later Tertiary strata north of Waltham 
Creek. Of the two possibilities the first seems the more probable. 

Wells have been drilled for oil at two places on the north side of 
Waltham Valley near the reported seep. Just south of the southeast 
corner of sec. 20, T. 20 S., R. 13 E., five wells were put down within 
a few hundred feet of one another 9 or 10 years ago b} 7 the Echo Oil 
Co. The deepest well, No. 2, is said to have been drilled to a depth 
of 1,400 feet. Two of the wells are said to have obtained small quan¬ 
tities of gas and oil, and it is commonly reported that as much as 5 
or 6 gallons of light-gravity oil has been bailed out at a time. About 
a mile to the southeast, near the center of sec. 33, T. 20 S., R. 13 E., 
is the Warthan Oil Co.'s well. Drilling has been carried on here at 
various times since 1909 but was suspended in September, 1913, for 
lack of funds. This well and those of the Echo Oil Co. are close to a 
large fault, along which the strata are steeply tilted and much frac¬ 
tured. If oil did occur in the rocks, it probably would have tended to 
migrate from the beds that lay relatively close to the fault into the 
crushed zone, but the position and attitude of the more distant rocks 
make it improbable that oil from any very great thickness of beds 
would have migrated in this manner. Also, the beds along the fault 
are so steeply tilted and so broken that they offer a ready avenue 
of escape to the surface for any oil which might be contained in them. 

BITTER WATER AND PEACHTREE VALLEYS AND FOOTHILLS TO THE WEST. 

GEOLOGY. 

West of the San Andreas fault zone the beds mapped as upper 
Miocene rest directly upon the eroded surface of the granite. In 
the area shown on the map these beds have a maximum thickness 
of about 3,300 feet and comprise two formations, of which the lower, 
made up of sand, clay, gravel, and diatomaceous shale and filled 
with marine fossils, is believed to be the equivalent of the Santa 
Margarita formation, and the upper, composed of material that was 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 145 

probably laid down in lakes or subaerially, is the equivalent of the 
Tulare formation. West of Peachtree Valley the upper of the two 
formations is relatively unimportant, appearing onl} r in isolated 
areas along the crests of the ridges as a cap less than 200 feet thick. 
The beds that are comprised in the formation that is considered 
the equivalent of the Santa Margarita are variable in character, 
ranging from coarse conglomerate to fine diatomaceous shale, but 
for the most part are fine grained. Near Lonoak and in Bitterwater 
Valley the lower 1,000± feet is composed of diatomaceous shale, 
which forms prominent white outcrops that are especially noticeable 
about 2 miles northwest of Lonoak post office. Shale of this type 
forms the lower part of the Tertiary along the west side of Bitter¬ 
water Valley, in the north end of Mustang Ridge, in small areas 
near the east corner of the Peachtree ranch, and in much of the 
Topo ranch northwest of the area mapped. In many other parts 
of the region, however, sandy or even gravelly beds, such as those 
exposed near the asphalt quarry west of Lonoak, rest upon the 
granite. Practically no diatomaceous shale appears resting upon 
the granite near its exposures in small areas 4 miles southwest 
of Lonoak. The variability in the lithology of the lower part of 
the Tertiary is well shown along the north side of San Lorenzo 
Creek west of the granite that is exposed at the edge of the area 
mapped. Possible explanations of the variability in the thickness 
of the diatomaceous shale appear to be (1) that the Tertiary beds 
were laid down upon a very uneven surface of granite and that in 
parts of the region the lower beds were not deposited; (2) that the 
shale actually grades laterally into coarser materials; (3) that the 
diatomaceous shale is older than the clay and shale and is separated 
from them by an unconformity. The most probable explanation 
seems to be that the variability in the thickness of the shale is due 
both to lateral variation in character and to the uneven surface upon 
which it rests. Sandy beds intercalated with the diatomaceous shale 
contain fossils apparently of precisely the same type as those in the 
overlying sandy beds, and it seems improbable that any considerable 
time intervened between the deposition of the two divisions. The 
presence or absence of the diatomaceous shale is of considerable im¬ 
portance, for the seeps of oil appear only in those areas where it has 
considerable thickness. 

The Tertiary strata that cover the granite have not been deformed 
to any very marked degree west of the San Andreas fault zone. West 
of Peachtree Valley nearly to the edge of the area mapped this cover 
may be thought of as a sheet, very slightly wrinkled along irregu¬ 
lar lines and in general dipping slightly toward the northeast. 
Farther west the dip changes; along the edge of Salinas Valley it 


146 CONTRIBUTIONS TO ECONOMIC GEOLOGY; 1913, PART II. 

is in general toward the west, carrying the beds beneath the valley. 
Between Peachtree Valley and the San Andreas fault zone is a shal¬ 
low syncline, which the writers have termed the Peachtree syncline. 
This fold starts near the center of the Peachtree ranch and continues 
northwest through the Topo ranch, beyond the area mapped. The 
east flank of this syncline is terminated by the San Andreas fault 
zone, along which the beds of diatomaceous shale in the lower part of 
the later Miocene formations are so tilted that .they are- nearly verti¬ 
cal. North of Lonoak the southwest flank of the syncline merges with 
the area of low irregular dips along the foothills east of the Salinas 
Valley, but along the Peachtree Valley it is apparently terminated 
by a fault. It is in this synclinal basin that most of the drilling for 
oil has been done. Along the San Andreas fault a zone varying from 
three-quarters to 1 mile in width is traversed by innumerable faults 
and the rocks are greatty shattered. In this zone rocks of the Fran¬ 
ciscan and later formations are intermingled in irregular masses, and 
along the west side steeply tilted beds of diatomaceous shale occur. 
Through this zone of fracture oil contained in the rocks has found 
an easy passage to the surface. Several wells have been drilled along 
it, but none of them have found any considerable reservoir of oil. 

SURFACE INDICATIONS OF PETROLEUM. 

In several places in Bitterwater and Peachtree valleys oil im¬ 
pregnates the surficial sandy beds that lie in the San Andreas fault 
zone or that rest upon the granite. The largest of these outcrops oc¬ 
curs at the Mylar asphalt quarry, in secs. 14 and 15, T. 19 S., R. 9 E., 
about 2 miles west of Lonoak. The basal 25 to 50 feet of the later 
Miocene here is a coarse, arkosic sand or grit that was evidently de¬ 
rived from the granite upon which it rests. The outcrops of this 
sand for a distance of about one-half mile are impregnated with tarry 
oil or asphalt, the amount contained varying from place to place. 
Where the outcrops are weathered and unbroken the sand is light 
brown and friable, but in the newer faces of the quarry the sand is 
plastic from the amount of tar it contains, and in one place thick oil 
slowly oozes out along its contact with the underlying granite. The 
oil sand or asphalt is quarried from time to time and used in repair¬ 
ing the roads about King City. Most of the sand is of medium 
coarse grain, and the material is used directly upon the roads with¬ 
out the addition of more sand. 

Oil-saturated sands outcrop at two places near the southeast cor¬ 
ner of the Peachtree ranch, in what corresponds to the SE. J sec. 22 
and the SW. J sec. 25, T. 20 S., R. 11 E. At the first-named locality 
a massive sandstone that stands almost vertical occurs on the west side 
of an area of much contorted diatomaceous shale. The relationship 
of the sandstone and shale is not entirely clear, as the rocks are con- 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 147 

siderably faulted, but the sandstone is believed to be stratigraphically 
above most or possibly all of the shale. The sandstone is impreg¬ 
nated with heavy oil, which slowly seeps out in the bottom of one of 
the steep arroyos. About 1£ miles southeast of this seep a sandstone 
50 to 60 feet thick, bedded with the diatomaceous shale that occurs 
near the base of the Tertiary, is impregnated with oil. This bed ap¬ 
pears to be a sandy lens in the upper part of the diatomaceous shale. 
It lies at the western edge of the San Andreas fault zone, is much 
fractured, and is truncated on the east by a fault that brings it into 
contact with the clay in the Tulare formation. 

Where the San Andreas fault crosses Alvarez Creek, in sec. 32, 
T. 18 S., R. 10 E., an outcrop of much fractured coarse arkosic sand¬ 
stone in the Tulare formation is stained by petroleum, and wells less 
than 100 feet deep sunk here have yielded a little light-gravity oil. 

About 13 miles due north of King City, approximately in sec. 
29, T. 17 S., R. 8 E., at the Matthews asphalt quarry, a bituminous 
sandstone outcrop lies, like that at the Mylar quarry near Lonoak, 
between outcrops of granite and of diatomaceous shale. This sand¬ 
stone may underlie the diatomaceous shale, as was suggested by 
Eldridge, 1 but as the oil sand is limited to the small gulch tributary 
to Clialone Creek and contains besides granitic material an appre¬ 
ciable number of diatomaceous shale fragments, the writers suggest 
that it is probably a stream terrace deposit impregnated with and 
cemented by thick tarry oil that seeped out of the lower part of the 
diatomaceous shale. The beds of sand and gravel impregnated with 
oil are of very uneven grain and on the whole are much coarser than 
those at the Mylar quarry. 

WELLS DRILLED FOR OIL. 

The following wells have been drilled for oil in and near Bitter- 
water and Peachtree valleys: 

Nonpareil No. 1, sec. 32, T. 18 S., R. 10 E. 

Nonpareil No. 2, sec. 32, T. 18 St, R. 10 E. 

Nonpareil No. 3, sec. 32, T. 18 S., R. 10 E. 

Lonoak No. 1, sec. 7, T. 19 S., R. 10 E. 

Lonoak No. 2, sec. 31, T. 18 S., R. 10 E. 

Alvarez No. 1, sec. 33, T. 18 S., R. 10 E. 

Le Franc No. 1 (Standard Oil Co.), Topo ranch, in what corresponds to 
sec. 33, T. 17 S., R. 9 E. 

Tompkins No. 1 (Standard Oil Co.), sec. 19, T. 19 S., R. 10 E. 

Tompkins No. 2 (Standard Oil Co.), sec. 19, T. 19 S., R. 10 E. 

Landrum No. 1 (Standard Oil Co.), sec. 28, T. 19 S., R. 10 E. 

Doheny well, sec. 14 or 15, T. 19 S., R. 9 E. 

Miller No. 1 (Union Oil Co.), Peachtree ranch, in what corresponds to sec. 
24, T. 20 S., R. 10 E. 

Salin as No. 1, sec. 9, T. 19 S„ R. l0 E. __ 

1 Eldridge, G. H\, The asphalt and bituminous rock deposits of the United States : U. S. 

Geol. Survey Twenty-second Ann. Kept., pt. 1, pp. 409—410, 1901. 

62083°—14-3 




148 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

The Nonpareil wells were drilled about 13 years ago near the seep 
where the San Andreas fault crosses Alvarez Creek. Previous to the 
drilling of the main wells, two wells were drilled by hand, the deeper 
of which is said to have obtained light-gravity oil at 60 to 70 feet. 
At the time of the writers’ visit it had caved below the 55-foot depth 
and was dry of oil, although containing considerable gas. Of the 
three larger wells, No. 1 is said to have reached a depth of 1,038 feet 
without obtaining more than a trace of oil. Well No. 2 was drilled 
653 feet and obtained oil between 400 and 520 feet. Oil now stands 
in the hole, but the well has never produced. Well No. 3 reached a 
depth of 1,300 feet, having been drilled through “ a great mixture 
of rocks,” but obtained no oil. 

Lonoak well No. 1 was sunk about 2,700 feet and is said to have 
reached granite at that depth without having encountered a trace of 
oil. Well No. 2 reached a depth of 3,009 feet, getting a little tarry 
oil at 600, 800, and 1,800 feet. A few barrels of oil is said to have 
been pumped. 

The Salinas well is said to have been drilled to 450 feet and at that 
depth to have found a little very heavy oil like that in Lonoak well 
No. 2. 

The Doheny well, near the southwest corner of sec. 14, T. 19 S., 
K. 9 E., starts about 750 feet south of the outcrop of the oil sand at 
the Mylar asphalt quarry. It is said to have reached the granite at 
900 feet without having found oil. The lack of success of this well 
is striking and shows the local character of the oil sand that is quar¬ 
ried as asphalt. 

The Alvarez well was started a few hundred feet south of the old 
Nonpareil wells and drilled to a depth of 900 feet but obtained no oil. 

The Le Franc well of the Standard Oil Co., at the head of Bitter- 
water Valley, within a few hundred feet of the San Andreas fault 
line, was drilled to a depth of more than 2,000 feet. It is said to have 
penetrated considerable oil sand but produced no oil. The fractured 
condition of the beds here prohibits an estimate of the stratigraphic 
position of the oil sands penetrated. 

The two Tompkins wells and the Landrum well of the same com¬ 
pany were drilled in Peachtree Valley and are said to have reached a 
“ hard gray sand ” without finding more than a trace of oil. It may 
be that the “ gray sand ” is an arkosic sand derived from the granite 
and is similar to that at the asphalt quarry west of Lonoak, but the 
writers believe that it is more probably granite. 

The Miller well of the Union Oil Co., near the west edge of the 
Peachtree ranch, along the road from Peachtree Valley to Salinas 
Valley was drilled to a depth between 2,500 and 2,600 feet, but no 
oil was found. 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 149 

ECONOMIC POSSIBILITIES. 

Along the San Andreas fault the beds are broken and all the 
formations are so intermingled in small irregular masses as to form a 
structure exceptionally unfavorable for the accumulation and reten¬ 
tion of petroleum. It is true that oil contained in the solid rocks in 
the immediate vicinity would probably work its way into the crushed 
zone, but it is difficult to believe that it would be held there in quan¬ 
tity and would not work its way to the surface. Thus, although seeps 
of oil occur along this zone, and although wells such as Lonoak well 
No. 2 and the Salinas well have obtained small quantities of oil, the 
presence of oil beneath the surface in sufficient amount to make drill¬ 
ing profitable seems very unlikely. Also, the experience in other Cal¬ 
ifornia fields shows that oil contained in rocks so badly fractured as 
these is of variable character and that much of it is of heavy gravity. 
Thus the oil found in the Lonoak and Salinas wells is probably typi¬ 
cal of the oil that does occur, despite the fact that small quantities 
of light-gravity oil have been found in shallow wells on Alvarez 
Creek. 

Of the 3,000 feet or more of Miocene beds which are infolded in 
the Peachtree syncline near Lonoak the lower 1,000 feet or so is 
largely diatomaceous shale. This shale is continuous southward but 
seems to become more sandy in that direction. That the beds asso¬ 
ciated with the shale contain some oil is shown by the outcropping- 
oil sands in the southeast corner of the Peachtree ranch and by the 
results obtained in the wells near the mouth of Lewis Creek. How¬ 
ever, the writers believe it doubtful that oil has accumulated here 
in any considerable amount. The syncline is structurally isolated, 
being bounded sharply on the east by the San Andreas fault zone 
and on the southwest by the granite and probably by a fault extend¬ 
ing along Peachtree Valley. Thus it seems improbable that oil 
could have collected in this basin from the rocks underlying any very 
extensive area. Any oil which might have been formed in the beds 
beneath Salinas Valley would probably not travel eastward beyond 
the area west of Peachtree Valley, in which the Tertiary beds are 
wrinkled irregularly. Moreover, except in a small area near the 
mouth of Lewis Creek, where the beds are slightly domed, the gen¬ 
eral synclinal structure is not favorable for the collection of petro¬ 
leum. Even the doming cited is really so slight and lies so close 
to the badly fractured San Andreas fault zone that it is improbable 
that oil has collected in it. The wells which have been drilled here 
have pretty thoroughly tested the area, and it is believed that fur¬ 
ther drilling, even along the small fold mentioned above, will fail 
to disclose any extensive accumulations of oil. 


150 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

The low foothills between the Peachtree and Salinas valleys present 
many of the features exhibited by the large productive fields in 
California, and in this area alone, of all the region studied, does 
there appear to be a possibility of obtaining oil. The factors sup¬ 
porting the theory that oil may have accumulated here in consider¬ 
able amounts may be listed as follows: (1) Some oil is undoubtedly 
present, as is shown by the outcropping oil sand at the asphalt 
quarry near Lonoak and at the south end of the Peachtree ranch; 
(2) diatomaceous shale, which is regarded as the ultimate source 
of the oil in this part of the State, is bedded with, overlain by, and 
underlain by porous sandstone, which, although mostly of rather 
fine grain, would serve as an excellent reservoir for oil; (3) the sandy 
beds are somewhat lenticular and are intercalated with clay or shale, 
thus probably furnishing local reservoirs of porous material more 
or less completely inclosed in impervious walls; (4) the beds are 
tilted slightly and irregularly, locally forming small, low structural 
domes; (5) to the west is the broad synclinal Salinas Valley, under 
which lies part at least of the thick mass of diatomaceous shale that 
outcrops along the Santa Lucia Range on the west side of the valley. 
Thus there is an area of considerable size from which oil might have 
risen to collect in the slightly folded rocks. 

Although the broader features of the stratigraphy and structure 
appear to favor the hypothesis that oil has accumulated in the foot¬ 
hills west of Peachtree Valley, two important questions remain to 
be answered, and to neither of them does the answer seem favorable, 
so far as may be judged from the areal geology. They are (1) whether 
the oil, though undoubtedly present, was formed in quantities in 
any way comparable with those found in the southern end of the 
San Joaquin Valley; and (2) whether, if any considerable quantity 
of oil was formed beneath the valley, it would have collected in the 
beds in the foothills on the east side in reservoirs of sufficient size 
to be commercially valuable. 

It seems probable that the first question must receive a negative 
answer. Seeps of oil and dry oil sands occur not only in the region 
described but also to the southeast, in the Parkfield region, and at 
intervals for several miles on the west side of the valley. In other 
words, the outcrops of the Tertiary rocks on both sides of the basin 
show evidence of petroleum, and it is reasonable to suppose that 
the beds in the center of the basin, now covered by alluvium, also 
contain or at one time contained it. The basin occupied by sedi¬ 
mentary rocks here is, however, of much smaller area than that at 
the southern end of the San Joaquin Valley; the diatomaceous shale 
in it is far thinner than that in the Temblor Range and along the 
east side of the Salinas Valley is somewhat irregularly developed, 
owing, in part, to its having been laid down upon a very irregular 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS^ CAL. 151 

surface of granite and probably also in part to the fact that it is 
replaced in some areas by sandy beds. This irregularity is well shown 
along San Lorenzo Creek. Near Lonoak the lower 1,000 feet or so of 
the later Miocene is fairly pure diatomaceous shale, but less than 2 
miles downstream sand and sandy clay, in lithologic character pre¬ 
cisely like the beds overlying the diatomaceous shale near Lonoak, 
rest directly upon the granite. Also, near the small granite ex¬ 
posures some 4 miles southwest of Lonoak the sedimentary beds 
are entirely sand and sandy clay. Thus if the diatomaceous shale 
is regarded as the ultimate source of the oil it is unreasonable to 
suppose that so great quantities of oil were formed here as were 
formed in the southern end of the San Joaquin Valley. 

The oil seeps in the region studied are very closely associated with 
the diatomaceous shale, and practically none is known in an area in 
which the shale has not considerable development. It is not unrea¬ 
sonable to suppose that beneath the alluvial filling in Salinas Valley 
the diatomaceous shale has as irregular a development as it has where 
exposed in the area studied. If such is the case, unless there is some 
special cause for its further migration, any oil which may have 
originated in the shale would probably not move farther than the 
sandy beds interstratified with or immediately adjacent to the shale. 
Thus the tendency would be for the formation of a number of small 
local concentrations. 

So far as the effect of the structure upon a possible accumulation 
of oil is concerned, the most notable feature in the foothills between 
Peachtree and Salinas valleys is the lack of any well-defined fold at 
all comparable with those which, south of Coalinga, border the San 
Joaquin Valley on the west and along which lie the productive oil 
fields. Instead of being strongly folded the Tertiary beds along the 
east side of Salinas Valley are but slightly tilted, in much of the 
area less than 2°. The importance of this difference in structure 
can hardly be overestimated in considering the possibility of oil 
having accumulated in considerable quantity. 

Along the edge of Salinas Valley the dip is in general southwest, 
but near the border of the area mapped it is northeast. The change 
does not take place along a line, but rather along an ill-defined belt 
several miles in width, or it perhaps may best be described as being 
marked by a number of short irregular domes of which three appear 
in the area mapped. One occurs near the asphalt quarry west of 
Lonoak, where the later Miocene beds dip 2° to 7° away from the 
o-ranite. The second occurs west of the Peachtree ranch, where a 

b _ 

line trending northwest-southeast through secs. 16 and 22, T. 20 S., 
R. 10 E., separates the beds that dip about 2J° SW. from those that 
dip approximately as much northeast. The third occurs just north¬ 
west of the isolated outcrop of granite some 4 miles southwest of 


152 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

Lonoak. These uplifts are so gentle that their axes can not well be 
designated by a definite line, but their position is indicated by the 
dips given on the map. 

In San Joaquin Valley the sandy beds along the anticlines have 
served as reservoirs for oil that is believed to have once been con¬ 
tained in beds that extended over large areas. Much of the oil prob* 
ably originated beneath San Joaquin Valley, worked its way up the 
rise, and accumulated in the upper parts of the folds. On the east 
side of Salinas Valley, however, no such folds dominate the struc¬ 
ture and there appears to be no reason why oil that may occur dis¬ 
seminated through the rocks over a wide area should accumulate 
in considerable amounts in a single small area. On the contrary, oil 
which may have originated beneath the valley would probably tend 
to remain in the upper parts of the numerous low, faint domes or 
wrinkles. Moreover, the diatomaceous shale is much thinner along 
Salinas Valley than it is along the western border of San Joaquin 
Valley; hence it is even more necessary in Salinas than in San 
Joaquin Valley that a structural feature which favors the accumula¬ 
tion of oil should have tributary to it a large area from which oil 
may be drained. 

In conclusion it may be said that the irregular structure, the ir¬ 
regular distribution of the diatomaceous shale, and the lenticular 
character of the sandy beds all seem to indicate not that oil has ac¬ 
cumulated in any considerable quantity in few localities but rather 
that it has accumulated in small amounts at a number of places in 
the upper parts of low folds or domes. It is not at all unlikely that 
wells drilled along the axes of the low anticlinal folds that lie be¬ 
tween Salinas River and Peachtree Valley will find oil. It is to be 
expected, however, that the area that may prove productive is very 
irregular in outline, and that the amount of oil in the producing wells 
will be small. Thus for many years to come the cost of prospecting 
this region with the drill will probably be much greater than the 
value of the oil that may be obtained. 

So far no well has adequately tested the area west of the Peach¬ 
tree Valley. The well most advantageously placed is the Miller 
well of the Union Oil Co., which was drilled near the southwest side 
of the Peachtree ranch, -about a mile east of the line of change in 
dip, in secs. 22 and 16. Although the test would have been more 
satisfactory had the well been located farther west, still the failure 
to obtain oil in it goes far to prove that any oil sands which may 
occur here are of small extent. Also, the outcrops of granite some 
4 miles southwest of Lonoak are significant, for although there is 
here a slight fold or dome comparable with that near Lonoak, yet 
the beds, unlike the Tertiary sands at Lonoak, show not the slightest 
trace of oil. 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 153 

OUTLYING DISTRICTS. 

The following brief notes regarding the geology and possible oc¬ 
currence of oil in the Topo ranch, which lies beyond the boundary 
of the area shown on the map, in the upper part of the valley of 
San Benito River, are based on hurried visits made during the course 
of the work. 

TOPO RANCH. 

The Peachtree syncline continues as a broad, shallow fold north¬ 
westward beyond the area shown on the map, passing through the 
Topo ranch. On the east the syncline is terminated by the San 
Andreas fault zone and on the west by the granite which here ap¬ 
pears at the surface in the Gabilan Range. Along the west side of the 
syncline the lower part of the Tertiary section consists of chalky 
white diatomaceous shale having a maximum thickness of not more 
than 1,000 feet. Upon the shale rest a few hundred feet of sandy 
beds, which constitute both the Santa Margarita and the Tulare 
formations. The beds for half a mile on either side of the axis of 
this syncline dip at angles of less than 5° and on the west flank of 
the fold at angles of less than 10° as far as the granite hills. The 
Matthews asphalt quarry (see p. 147) is on the west flank of this syn¬ 
cline at the contact between the granite and overlying Tertiary beds. 

Five wells have been drilled by the Standard Oil Co. in this syn¬ 
cline on or south of the Topo ranch. Some of them were drilled 
through the Tertiary beds to the underlying granite, but none found 
more than a trace of oil or gas. Their names and location are given 
below: 

Dunne No. 1, Topo ranch, west of Dunne ranch house. 

Dunne No. 2, Topo ranch. 

Brown No. 1, sec. 15, T. 17 S., R. 8 E. 

Stone No. 1, sec. 27, T. 17 S., R. 8 E. 

Leonard No. 1, sec. 28, T. 17 S., R. 8 E. 

The Leonard well, drilled about one-third of a mile east of the 
Matthews asphalt quarry, started in the diatomaceous shale -and 
struck heavy oil and tar not far above the granite. 

This synclinal basin in and north of the Topo ranch presents few 
features which would make it appear probable that oil has collected 
in it in considerable quantity. It is isolated, being bounded sharply 
on the northeast by the San Andreas fault zone and on the west 
by the granite of the Gabilan Range, and is thus almost cut off from 
the Tertiary rocks in Salinas Valley. These conditions make it 
difficult to believe that the syncline has acted as a catchment basin 
for oil drawn from great stretches of rocks in the surrounding ter¬ 
ritory. Moreover, the synclinal structure is not especially favorable 
to the concentration of oil, as any oil that did exist in this rock would 


154 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

be forced up the rise and would appear at the surface, as it has at 
the Matthews asphalt quarry. Finally the wells that have already 
been drilled have pretty thoroughly tested the area. 

SAN BENITO RIVER VALLEY. 

East of San Benito River, near the southwest corner of T. IT S., 

R. 10 E., later Miocene beds, approximately the equivalent of the 
Etchegoin formation of the Coalinga region, dip rather regularly 
20°-30° SW. About a mile northeast of the area mapped these 
beds are broken by a fault which is approximately parallel to the 
San Andreas fault*. A short distance northeast of this fault Cre¬ 
taceous, Eocene (?), and Franciscan (Jurassic?) rocks appear. The 
upper part of the Miocene beds is mainly massive arkosic sandstone 
filled with marine fossils. Beneath these beds are alternating beds 
of reddish and greenish clay and gravel, much like the beds that 
appear along the axis of the Vallecitos syncline, about 10 miles away 
on the opposite side of the Diablo Range, and presumably of upper 
Miocene age. 

There seems to be no reasonable chance of obtaining oil in this 
part of the San Benito River valley. So far as known no seeps of 
petroleum occur here, although the rocks are broken and are in 
places much shattered by faults, so that oil certainly would have 
had abundant opportunity to reach the surface if it ever had been 
present. Also, so far as known, no masses of sedimentary rocks that 
contain any considerable amounts of organic material, such as dia- 
tomaceous or carbonaceous shale, occur in this region. Finally, the 
structure is not especially favorable to the accumulation of oil. 

It has been said that the value of this region as oil-producing ter¬ 
ritory is shown by the fact that it lies midway between Bitterwater 
Valley and the Vallecitos, in both of which seeps of oil occur. 
This can hardly be considered a valid argument, as the area is sepa¬ 
rated from the Bitterwater region by the San Andreas fault and 
from the Vallecitos by a. great mass of Cretaceous and Franciscan 
(Jurassic?) rocks, which lie stratigraphically below the oil-bearing 
rocks. 

The McMurtry-Hoeppner well, near the west line of sec. 32, T. IT 

S. , R. 10 E., is on James Creek, a tributary of San Benito River from 
the northeast. The well starts in the fossiliferous late Miocene beds 
and, when visited in November, 1913, had been drilled to a depth 
of 1,462 fee>t and had apparently reached the clay and gravel that 
form the lower part of the upper Miocene. No trace of oil had been 
obtained. 


OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 155 

COAL. 

OCCURRENCE AND AGE. 

Coal occurs in the Tertiary beds in the Priest Valley syncline and 
at several places in the hills on the south side of Waltham Valley. 
About 4 miles south of the summit of Smith Mountain is the 
Stone Canyon mine, at which coal has been mined at irregular inter¬ 
vals for many years. The coal beds within the boundaries of the 
area shown on the map have been prospected at a number of places, 
but when visited in the later part of 1913 none of the prospects 
remaining open furnished a good section of the beds and no fresh 
samples of the coal were obtained. Although no attempt was made 
to study the coal beds in detail, the following facts, which were 
brought out in the course of the work, regarding the age of the 
different carbonaceous beds and their general distribution are be¬ 
lieved to be of sufficient importance to record. The points of chief 
interest are that coal occurs at three horizons in this part of the 
Diablo Range—in the Eocene, the lower Miocene, and the upper 
Miocene; that the coal in Priest Valley is not, as is commonly 
thought, the same as that in Stone Canyon but is younger and ap¬ 
parently of much poorer quality; that the coal occurs in small isolated 
structural basins and not, as has been reported, in a continuous 
bed or succession of beds extending from Stone Canyon northwest¬ 
ward to the valley of San Benito River. 

EOCENE COAL. 

Coal occurs in Eocene beds exposed west of Coalinga and was 
mined there some 20 years ago. In 1893 approximately 400 tons were 
shipped, principally to Fresno, from the San Joaquin Valley and 
California mines. 1 The enterprise, however, did not prove profit¬ 
able, and mining was discontinued even before oil was discovered 
in the region in quantity. 

The coal occurs in the white quartzose sandstone of the Tejon 
formation in thin, discontinuous beds, most of them less than a foot 
thick, although it is said that the “big vein” in the old mines is 
about feet thick. 

Coal occurs in the Eocene sandstone (Tejon formation) at many 
places along the foothills on the east side of the Diablo Range north¬ 
westward from Coalinga, but principally on the south side of the 
Vallecitos in T. 17 S., Rs. 11 and 12 E. On the west side of the sum¬ 
mit of the Diablo Range in secs. 20 and 21, T. 17 S., R. 10 E., 2 miles 
north of the area shown on the map, is the Trafton mine, which 

i California State Mining Bureau Twelfth Rept. California State Mineralogist, pp. 50-54, 
1894. 


/ 



156 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 

was described briefly by Campbell. 1 The coal occurs in sandstone 
that, as nearly as could be determined in the brief time spent in the 
region, occupies about the same stratigraphic position as the coal- 
bearing beds in the Vallecitos, some 6 miles to the east, and, although 
no diagnostic fossils were found in the coal-bearing beds, the coal 
at the Trafton mine is probably of Eocene age. 

LOWER MIOCENE COAL. 

The coal at Stone Canyon, in the center of T. 22 S., R. 13 E., has 
been described briefly by Arnold 2 and Campbell. 3 It occurs in the 
lower part of the Vaqueros formation (lower Miocene) close to the 
contact with the Cretaceous rocks and the Franciscan formation 
(Jurassic?), upon which the Vaqueros rests unconformably. On the 
opposite (northeast) side of the Diablo Range the lower part of the 
Vaqueros is exposed in the area discussed in the present report on 
both flanks of the syncline that trends northwest on the north side of 
Smith Mountain. The lower beds are best exposed on the south 
flank of the syncline from the head of Jacalitos Creek, in sec. 35, T. 21 
S., R. 13 E., northwestward through secs. 34, 33, and 28, and on the 
north flank of the fold in the NW. 1 sec. 21 of the same township just 
west of the trail that leads from Waltham Valley to Bourdieu Valley. 
In both places the beds are rather steeply tilted, dipping 40°-75°. 
These dips are, however, restricted to a relatively narrow belt, and 
in much of the intervening area, closer to the axis of the syncline, 
the Vaqueros is tilted less than 30°. 

The coal-bearing portion of the formation lies below the massive 
calcareous sandstone which outcrops along the crest of the ridge 
and which forms the top of Smith Mountain and Smith Pinnacles. 
It varies greatly in thickness and in character and is evidently a 
near-shore deposit that was laid down upon a very uneven surface 
of Franciscan, Knoxville, and Chico rocks. This part of the Va¬ 
queros weathers easily and, occurring as it does beneath a massive 
cliff-forming sandstone, furnishes few good exposures. At the head 
of Jacalitos Creek, in the SW. J sec. 35, T. 21 S., R. 13 E., the beds 
beneath the massive calcareous sandstone have a thickness of at 
least 200 feet. The upper 100 to 150 feet is composed of beds of 
greenish or bluish conglomerate formed largely of fragments of 
Franciscan rocks, beneath which is 75 to 100 feet of carbonaceous 
and perhaps in part diatomaceous shale. The outcrop of this shale 

1 Campbell, M. R., Coal in San Benito County, Cal. : U. S. Geol. Survey Bull. 431, p. 
243, 1911. 

2 Arnold, Ralph, Coal in the Mount Diablo Range, Monterey County, Cal. : U. S. Geol. 
Survey Bull. 285, pp. 223-225, 1906. 

3 Campbell, M. R., Coal of Stone Canyon, Monterey Countv, Cal. : U. S. Geol. Survey 
Bull. 316, pp. 435-438, 1907. 



OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 157 

is apparently terminated on the south by a fault that has brought the 
shale into contact with sandy shale and somewhat concretionary sand¬ 
stone whose exact stratigraphic position is not known. The car¬ 
bonaceous shale is, however, not far above the base of the Vaqueros. 
On the north side of this syncline, in the NW. J sec. 21, T. 21 S., 
Iv. 13 E., the following section is exposed. The thicknesses given are 
estimates but are probably accurate within 10 per cent. 

Incomplete section of carbonaceous heels in lower part of Vaqueros formation in 

NW. i see. 21, T. 21 8., 1Z. 13 E. 

Feet. 

A. Sandstone, massive, somewhat calcareous; basal bed 
tilled with large oyster shells. Probably the lower part 


of the sandstone that forms Smith Pinnacles. 

B. Sandstone, less massive than bed A, light gray, weather¬ 

ing to yellow-brown_ 10 

C. Sandstone, somewhat carbonaceous, rather shaly, weather¬ 

ing red-brown. Bed 1 foot thick 6 feet above base is 
filled with large oyster shells_ 16 

D. Sandstone, light gray, not notably carbonaceous_ 21 

E. Sandstone, somewhat shaly and carbonaceous, like bed C_ 4 

F. Conglomerate and clay, reddish, purplish, and greenish. 

Purple beds almost wholly minute fragments of ser¬ 
pentine and basic igneous rocks. Pebbles largely flat 
fragments of Franciscan, rarely over 3 or 4 inches 


long-35-40 

G. Sandstone, mainly shaly and carbonaceous, with a few 
massive concretionary beds. Somewhat like bed E. 

Base not exposed_=_ 15+ 


The beds lying beneath the coal and mapped as part of the 
Vaqueros formation have not yet yielded diagnostic fossils. At the 
Stone Canyon mine the coal rests upon clay shale somewhat different 
from any beds of the Vaqueros above the coal, and judged by this 
section alone there seems to be some ground for the view held by 
many who have examined the mine that the clay and coal are parts 
of a formation older than the Vaqueros. However, on the northeast 
side of the Diablo Range the carbonaceous beds are underlain in 
places by gravel and coarse sandstone precisely like those which 
overlie the coal and which contain typical lower Miocene fossils. 
Thus there seems to be no reason to doubt that the coal is of lower 
Miocene age, as it was regarded by Arnold. 1 

Several prospect tunnels have been run into the lower part of the 
Vaqueros in the north half of secs. 33 and 34, T. 21 S., R. 13 E., in 
the valley of a stream tributary to Alum Creek. According to Mr. 
V. IT. Crump the last work here was done in 1909, when a San Jose 
company ran a 200-foot tunnel to crosscut the coal. The tunnel 

1 Arnold, Ralph, Coal in the Diablo Range, Monterey County, Cal.: U. S. Geol. Survey 
Bull. 285, pp. 223-225, 190G. 









158 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1913, PART II. 


started in beds a little below the massive calcareous sandstone of the 
Vaqueros and ran south about 200 feet into the Franciscan forma¬ 
tion without finding coal. On the west side of the same creek near 
the line between secs. 33 and 34 are other caved prospect tunnels, 
which, to judge from the dump, were at least 200 or 300 feet in 
length. No definite information was available concerning them, but 
fragments of coal and carbonaceous shale lie in the dump. On 
the east side of the creek a prospect having about 200 feet of tunnel 
and incline was dug by Mr. Crump eight or nine years ago. 

UPPER MIOCENE COAL. 

Carbonaceous shale and thin beds of coal occur in the western 
end of the Priest Yalley syncline, in T. 20 S., P. 12 E. On the south 
flank of the syncline outcrops of very carbonaceous shale and of 
coal are traceable from the southwest corner of sec. 25 northwestward 
through secs. 26, 2T, 22, 21, and IT to the center of the S. \ sec. 8, 
and thence eastward through secs. 9, 10, and 11 nearly to the center of 
sec. 14. The easternmost outcrop of these beds that was discovered 
on the north flank of this syncline occurs along the divide between 
Priest and Waltham valleys, although carbonaceous beds are re¬ 
ported to outcrop about a mile southeast of that divide, in the N. -J 
sec. 24. 

The carbonaceous beds occur within 1,500 feet of the top of the 
upper Miocene. About 150 feet above them is a fossiliferous zone 
that contains abundant specimens of the scallop shells Pecten wattsi , 
Pecten nutteri , and Pecten coalingensis and of Thais ( Purpura ) 
etchegoinensis. This fossiliferous zone occurs in the upper part of 
the Etchegoin formation in the Coalinga region. For the most part 
the carbonaceous beds form poor outcrops, weathering character¬ 
istically to a loose, deeply cracked clayey soil that supports a some¬ 
what better growth of grass than the more sandy beds. They are 
probably best exposed south of Priest Valley post office, where the 
following section was measured: 


Section of carbonaceous beds in NE. 1 sec. 21, T. 20 S., R. 12 E., a quarter of a 

mile south of Priest Valley post office. 

Feet. 

Sandstone, massive, gray, cross-bedded; fossiliferous zone con¬ 
taining Thais ( Purpura) etchegoinensis, etc., in lower 50 feet_ 275 


Shale, greenish brown; contains numerous ironstone concre¬ 
tions and a thin bed of lignitic shale near base_ 60 

Sandstone, reddish gray, concretionary, poorly consolidated_ 8 

Shale, friable, greenish, stained reddish by iron_ 11 

Shale, brownish, carbonaceous, very fissile_ 5 

Shale, drab, carbonaceous_._^_ l 

Shale, brownish red, carbonaceous_ 3 







OIL PROSPECTS IN WALTHAM AND OTHER VALLEYS, CAL. 159 


Feet. 


Shale, bluish, soft and fissile_ 

Shale, brown, carbonaceous_ 

Sandstone, gray, interstratified with fissile gray shale_ 

Shale, soft and fissile; alternating bluish and brownish beds. 

Sandstone, somewhat pebbly; a few thin beds of brown shale_ 

Shale, gray, iron stained; contains 2 to 4 inch beds of carbo¬ 
naceous shale_ 

Shale, brown, carbonaceous; thin partings of bluish shale_ 

Not exposed (shale?)_ 

Shale, poorly exposed; contains at least one bed of carbo¬ 
naceous shale 2± feet thick_ 

Shale, bluish gray, iron stained_ 

Shale, brown, carbonaceous, with streaks of coal_ 

Shale, light gray_ 

Shale, carbonaceous, with streaks of coal_ 

Shale, light gray, iron stained; bed of carbonaceous shale 

1 foot thick near middle_ 

Sandstone, yellowish, concretionary_ 

Shale, brownish, carbonaceous, with streaks of coal_ 

Shale, light gray, with yellowish concretionary layers_ 

Shale (?); exposures poor but apparently show alternating 
thin layers of clay shale and carbonaceous shale; fairly 
definite 10-inch bed of brown carbonaceous shale near base_ 

Shale, light gray, iron stained- 

Shale, brown, carbonaceous, with streaks of coal- 

Not exposed (shale?)- 

Shale, light gray, iron stained, increasingly sandy toward 

base_ 

Sandstone, gray, iron stained, massive, cross-bedded. 


4 
6 

15 

15 

65 

TO 

6 

TO 

12 

28 

5 
3 

12 


85 

T 

2 

15 


25 

20 

3 

20 

100 


951 


The coal beds in the Priest Valley syncline have been prospected 
at three places—in Coal Canyon, which is a tributary of Waltham 
Creek; in sec. 21, south of Priest Valley post office; and in sec. 17. 
The following notes regarding these prospects were obtained mainly 
from Mr. Thomas Hart, of Priest Valley. 

The first prospecting was done about 20 years ago by Hart & 
Drabble on the north side of Coal .Canyon, in sec. 22, T. 20 S., R. 12 E. 
They ran a 60-foot tunnel, known as the Drabble mine, in what they 
called the “ small vein,” a bed 3 or 4 feet thick in the upper part of 
the carbonaceous zone, which is rather sharply separated from the 
main part of the zone by gray sandstone. About 2 carloads of coal 
was taken out and hauled to the railroad. The mine was then sold 
to a Mr. Bush, of Hanford, who ran a crosscut, starting a few hun¬ 
dred feet below the Drabble tunnel. This crosscut was about 390 
feet long in 1893 and had penetrated the following beds: 1 


1 California State Mining Bureau Thirteenth Kept. State Mineralogist, p. 53, 1896. 























160 CONTRIBUTION'S TO ECONOMIC GEOLOGY, 1913, PART II. 
Beds penetrated in crosscut in Coal Canyon, Cal. 

Feet. 


Soft gray sandstone_200 

Light-blue compact clay_ 52 

Coal bed No. 1, carbonaceous shale and seams of coal- 4 

Soft gray sandstone and shales_ 28 

Gray compact argillaceous shale_ 7 

Coal bed No. 2, coal and seams of shale_ 3 

Sandy shales, passing into clay shales- 96 


390 

No more work was done until about 1907, when a company com¬ 
monly known as the Monterey Coal Co., or the Pacific Coal & Clay 
Co., dug a 115-foot slope and a 35-foot tunnel in the ravine west of 
the old Bush and Drabble prospects. South of Priest Valley post 
office, in the NE. J sec. 21, the same company dug a 60-foot slope and 
a 115-foot shaft, with 75 feet of drift at the bottom. In sec. 17, west 
of the post office, small pits have been dug along the outcrop of the 
coal. According to Mr. Hart, the coal weathers down rapidly into 
small platy fragments. 

In secs. 20 and 21, T. 19 S., R. 11 E., about 4 miles southeast of 

Hepsedam, carbonaceous shale and thin coaly beds underlie an area 

of a little over half a square mile in a small syncline. These beds 

occur a few feet below the fossiliferous sandstone filled with Pecten 

wattsi that occurs above the coal in Priest Valley. A tunnel, which, 

according to Mr. Hart, is about 600 feet long, dug by the Pacific Coal 

& Clay Co., starts in beds that lie stratigraphically below the main 

carbonaceous beds but probably crosscuts them. At the time of 

visit this tunnel was not open and no coal was seen in the dump. 

% 

o 










U. S. GEOLOGICAL SURVEY 
GEORGE OTIS SMITH, DIRECTOR 


BULLETIN 581 PLATE V 


12100 R. 9 E. 

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Alluvium and terrace deposits 

UNCONFORMITY 

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Sea. level 


Tulare formation 
i Light-colored arkone sandstone 
and shale-pebble beds \ 

UNCONFORMITY 

7Z 


////X 


Scale 96.ooo 

2 


5 Miles 


l Vz o 


1 


5 Kilometers 


R 


\ 


E 


7T 



\ 


u 


y 






V 


sr 


» 

/ 


y 







M/. 




V/M 


71 V 


/ 


/ 


R. 9 E. 


R. 10 E. 


121 


119 


117 


36 


\ xif 

\\ /Vt 

V-'L.. /> oaliiigaV;' * 1 

’ti 

, • ", McIfittndX 

> 


o 

V—a 




v- 


c 

1 —-— ? 

* 

o 


c> <=» 

y* 

As 



< 


% 


Y- 


c- 


y 






/ 


y/ 


/ 


77 




A 

/ <n. 









s’ 


— 36 


-34 


....y 


4-4 


\ 


•v,.. 

**7rr. r» ; 


/ 


V. 


c 

T 


lJL 


1914 


Chiefly upper Miocene 

(Northeast of San Andreas fault, fine-grained sandstone, 
sandy shale, massive blue sandstone, and conglomeratic 
beds, equivalent to the Jacalitos and Etchegoin formations 
of the Coalinga region and embracing in lower part some 
beds of probable middle Miocene age. Southwest of San 
Andreas fault, diatonuiceous and clay shale, sandy shale, 
sandstone, and shale-pebble beds, regarded as equivalent to 
Santa Margarita formation [middle Miocene 1 of the Salinas 
Valley) 


71 


U 






/ 




\ 




Y. 


18 





EXPLANATORY 


R.13 E. 


’ Anticline 


t Syncline 






\ 



Fault 

Contact of jacalitos and F.tchegoin 
formations in Coalinga region 

_ _ _ _ £Qal_ _ _ __ 

Outcrop of upper Miocene coal beds 

Productive oil wells 


Idle, abandoned, or drilling well 
X 

Oil seep or outcrop of oil sand 
Strike and dip 

K 

Strike and dip 
of overturned bed 

© 

Horizontal bed 



Santa Margarita ? formation 

( Diatomaceous and clay shales) 
UNCONFORMITY 



Vaqueros formation 

\Massive grayish arkost. sandstone. calcareous 
sandstone, and locally carbonaceous shale 
UNCONFORMITY 



Shasta series (Lower Cretaceousi and 
Chico formation (Upper Cretaceous) 

{Dark clay shales, massive arkose sand¬ 
stone, and coarse conglomerate > 
UNCONFORMITY 
77^77 


,7/'.' / 7/ err 
'/////SS/s, 
,'//s ' S/ ssr S 


Franciscan formation 
( Sandstone, shale, and chert. For 
convenience of making rarious younger 
intrusive rocks and small areas of 
Cretaceous rocks are included > 



c 

Elevation 
in feet 


2251s 

IPfk 


OD tP ■00 


121 ° 


119“ 


117 ° 


index map 

Showing location of the area mapped and described in this report 
50 0 50_100 Miles 




Sea level ■ 
- 1,000 ■ 


Slack Jjj 
Canyon p 

$ 

8 1 

$ 



if 


w 



Waltham 

Valley 


Itei 





Sea level 


SECTION ALONG LINE C~C 



3X 


Granite 

and associated schistose rocks 


R. 1$ E 


~V 


-v 


yXA 


v 



Coalin' 




A 




's/",:s/s,s. 

/ / / /f s y // 





''V/Z'S'i* 

t / // 'jS' ' 

/ / / / 


yy'7 






\ 


\'/e / A '/ 

' ' / / // ez / . / / / a / / v 
VS/S 


■ '/./ 'S/S, 
V/., '//,,/ 


'' /,/* "■ ■ 

kse,/ 


' X ' s ls' 

■/v,, , is 




zz tyy 




mm 


SOUTHERN 


a 




-J 


121°00' 


R. II 


R. 12 E.40' 


/ 


PACIFIC 


r 




Y 




!X.. 


10 


</) 


R. 13 E. 


R. 14 E. 


H 




30, 

00 


15 E. 120°20' 


<no»avu> ahd r*umo ivmi u vseikoaiou suwvtv 


Base from Priest Valley and Coalinga topographic sheets 
U. S. Geological Survey 


GEOLOGIC MAP OF THE WALTHAM, PRIEST, BITTERWATER, AND PEACHTREE VALLEYS, IN CENTRAL CALIFORNIA 


Geology by Robert W. Pack and Walter A. English 


NOTE.—The area map¬ 
ped as Santa Margarita? 
in secs. 2,3, and 11,T. 20 S.. 
R. 12 E., west of Center 
Peak, should have been 
shown as Franciscan 

























































































































































































































































































































































































































































































































































































































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